A Rudimentary Treatise On Geology

A

RUDIMENTARY TREATISE

GEOLOGY:

TOR THE USE OP BEGINNERS,

J

LIEUT. -COLON EL POHTLOCK . R. E.,

r. R. r.G. M K. I.A.. Ac.

r*a«if»RftT or tsi oioiostc a l locurv or seiui,

*•»

ctviiius or cost.

THIRD EDITION.

Ualm :

JOHN WEALE.

architectural library, 59, high holborm.

H.DCCC.L1*.

PREFACE TO SECOND EDITION.

An edition of more than 7000 copies having been sold of
this little volume, I have endeavoured to introduce such im-
provements into this, the second edition, as arc compatible
with its form and object. In doing so, 1 have availed myself
of some valuable suggestions of my friend Mr. Smith, of
Jordan Hill, regretting at the same time that a limited space
would not allow inc to give a perfect analysis of bis re-
searches In Pleistocene and Post -Tertiary Deposits. If the
labours of Travellers and Voyagers produce every year some
new additions to our knowledge of the existing creation, can
it be doubted that the Geologist, who is, as it were, a
traveller in ancient worlds, must equally discover new and
interesting farts f Geology is indeed a progressive science,
which, although it lias already produced much fruit, still
continues to promise an abundant and never-failing harvest
to those who diligently and skilfully cultivate it, — a truth
which has been powerfully illustrated within the last few
years, during which it has been shown that the highest type
of organic beings, the mammalia, appeared on the earth so
early as the Trias, — and still more recently whilst the last

T1 PftKFACt TO TBS SECOND EDITION.

sheets of this work were passing through the press, by the
fact tnqpunced by Sir C. Lrell, that the foot-marks of a
fresh-water tortoise had been diacoTcred some yean before
in the Silurian strata of Canada, and by fresh examples of
dicotyledonous plants in the Cretaceous strata, — thus unfold*
ing most remarkable resemblances between the physical con*
ditions of the earth at the most remote epochs and those
it now exhibits. What an incentiTe then is held forth to
the labourer in such s held, when to him may he allotted
the triumph of penetratiug still further into the mysteries
of Nature, and di»covrring new relics of the animals and
plants of extinct creations !

Woolwich.

Jmsstt. ISM.

J. E. P.

CONTENTS

CHAPTER I.

IWTIODOCnON. " 1 JKaycefenoe or Prwrtiet uu) Theor y mu*t be conblwd
for ibe *occ*a*ful progrra* of all Science, and for the perfect develop-
meat of Art . . . . 1— 15

CHAPTER II.

Csoloot — ) t» Meaning, Object, and I’tility a» a Science . . lb— 37

CHAPTER III.

Grolooical FoaMATiox* — Their Meaning. Object, and UUIlty — The
Mode of Studying them, and the Phjraioal Plienomena they exhibit —
Phenomena of Rock* — Stratification— Flciure* and Contortion* of
Strata — Cleavage (Joint -like and Slaty) — lienudation and Wear —
Fault* — Further Effect* of formative and destroying Uomi a* exhibited
in modem am) ancient Sea Cliff*, Sea Hear he*, Glacier*, and Ice-
berg* OS— C2

CHAPTER IV,

Platonic, Met amorphic, and Volcanic Rock* — Condition and Temperature
of the Interior of the Earth— liyke*— Elevating Foroea— Vein*—
Metallic DepuaiU — Economic Value and Lee* of the Ro ch a described

13—100

CONTENT®.

Tiii

CHAPTER V.

Foa«U» — Petrifaction* — Condition* of PeinArd Bodie*, tod Wod« of
Petrifaction — Petrifying 5gb*Uoo» — Di*tnhutkmuf PoaaiU,^. 101 — 125

CHAPTER VI.

General tod Practical Remark* on Urological Formation* — Cambrian, the
etriifit known FomiI Urfnxt.it — Silurian — Devonian, or Old Red Sand*
*Um+ — Carbonifrrou* — Permian, mrludmr Majrtieaian Limeatonc —
Nna Red or Tna* — Eta* Order — Oolue or Jura Formation

— WeaJden Formation — ( rrtareou* — Trrttary C'ia»« of Formation* —
Eocene, Miocene, and Pliocene lurmitmn* — Quitrman , P<nl Trrtury
or Po*t • Pliocene — Recent — Oirmirai I>cj*oa»t* — Organic Formation*

125— ISO

CHAPTER VII.

Tlieorir of Sjmnp

IM-190

CHAPTER VIII.

Concluding Remark*

191 — 196

RIDIM i:\TAUY OKOLOOY.

rilAITKH 1.

ImnmTtlflX — Ej')*rrtrnr* or Prttrttrr itnii Tktnry mint lx* CtimbtnH
(or Ihc progr**** of ft.il >t'irr. rr. Amt lor thr j*rrlVet ilrvrloju.

mrtil of Art.

As it is hojwd that t\\i% lit tla* Ih« k tuny lx* read by runny
member* of that valuable * of person-* who are railed prac-
tical nidi, it appear* drsiraMr to use it a* nn instrument for
dispelling fr<»rn their minds tin* prejudice they !<xi often
entertain against other men called scientific, and nt the an me
turn* for supjmrtitig their own claim to the eat iron t ion

of men of science, which, a* their most powerful auxiliaries,
they *o fully mrrit. The rniitunl distrust between scientific arid
practical men, though decreasing, doe* *till exist, and is to bo
ascribed, as in most human difference*!*, to the misapprehen-
sion or misinterpretation of a term, which term is in this case
4 Science.* What then dor* the term Science actually signify f
— simply knowledge: which may be viewed in two different
lights, and be understood as implying either

A Knowledge of Facts, the result of observation ; or
A Knowledge of Laws, obtained by reaaotiing cm com-
bined facts.

If tbeae divisions be kept in view, it will be admitted that
every human being must make more or less program in the
first branch of knowledge, as it is impossible to live and not to
acquire some experience of facts ; but that few, in comparison.

mpmCKtAIY GEOLOGY.

n

enter upon the second, which requires, in addition to oWm-
tion, a j»ower and a habit of reflection. And yet, however
exalted tliia exercise of the higher quality of reasoning must
intellectually he considered, it cannot dispense with that of
observation, as every attempt at mere speculative reasoning
baa only led to mysticism, and retarded the pr<>gress of that
real knowledge which proceeds cither directly or indirectly
from observed facts.

When the comparison of observed facts has led to the dis-
cover)' of a law or rule according to whirh those facts are in
connection one with t lie other, the mind acquires a power of
extending or developing the law itself tieyond the limits of the
observed facts ; and thus is enabled to advance into new
regions of inquiry, and to foretell facts which have yet to be
observed. And m like manner, the law or rule which has
been aveertainrd to connect together one set of facts, may be
found to agree with or even diqtcnd upon a law which connect!
together another set, the more comjKUind law being thus
traced up to the simple ; ami laws which from the different
nature of the oltsrrved facts may have been deemed in-
depmdent of each other, are brought into connection by being
rrferml to wnne more simplr law of which they are all proved
to hr developments.

Professor Lloyd (' Lccturr* on the Wave Theory of Light 1 )
has illustrated this subject. “ You are aware/* he says,
'* that in one mode of studying that interesting science.
Astronomy, the laws of Kepler are assumed as fundamental
principles, and from them, when unfolded, all the more ob-
vious apj»earanccs of the planetary system are deduced. In
Phyaical Astronomy, on the other hand, the laws of Kepler
themselves are derived as consryttemew* of a jtrimortfitf imw of
maitrr , and the development of this higher principle baa
brought to light a multitude of other laws of the universe,
which mere observation could hare never reached . 0 The n a me
of Kepler suggests bow instructive his example ought to be
when as a practical man he b o bserv ed, submitting hb pee-

HVDIMEVTAHY GEOLOGY. 3

Jttdk** to the test of experiment, and, hr diligently following
the movements of the planet Mars, and patiently comparing
together iti successive places, acquiring eridence that the
orbit or curve in which it moved round the »un was not a
circle but an ellipse, the sun being in one of its fbci. This
law of elliptic motion, and Kepfcr’s two other laws, haring
been generalized and connected ns necessary consequents with
the elementary laws of matter, the range of observation was
expanded over the whole material universe ; and when, from
the independent study of the motion of earh planetary body,
the Astronomer turned to the still more difficult investigation
of the mutual action of one upon the other, and finally over-
came and reduced to order all its difficulties, the Theoretic
Astronomer was enabled, in the person* of Messrs. Adams
and Lc Vrnricr, to advance before the observer, and to direct
him where to look for a remote and until then undiscovered
planet, * Neptune,* the existence of which they had inferred,
by calculation, from its perturhaling rffeett on other planets.
To this noble result of patient practical observation, combined
with and matured by study and reflection, M. Le Verrirr has
added another illustration of the aid derived by the practical
observer from the labours of the theorist, by determining the
elements of Faye’s comet within definite limits, and thereby
leading to its rediscovery by Professor Challi* at Cambridge,
cm the 28th of November, 1 850. This body, which had been
teen before in 1843—1, is, from the passage of its orbit
through that of the planet, subject to great perturbation
from the planet Jupiter ; and whilst M. Verrier, by calcu-
lating the amount of such perturbation, was enabled to trace
the course of the comet through a disturbed orbit, he did not
lfcil to perceive and to point out that the variation of the orbit
itself will finally Wad to a better appreciation of the disturbing
force, or to a more correct determination of the mass of
Jupiter : and similar illustrations might he multiplied from
tide one Science of the rid afforded to each other by tha
Observer sod the Theorist.

of the progressive movement of light was discovered prac-
tically by Hoerner, when observing the eclipses of Jupiter’s
satellites, as he found that the mean time of the emersion of
a satellite from the shadow of Jupiter’s body was greater or
less according as the distance of the earth was greater or less
than its mean distance from Jupiter, such difference being due
to the different times occupied by light in passing through the
resjK'ctive distances.

Ily a number of companion* of the times of the emersions
of Jupiter’s satellites in the varying jxjaitions of the earth, it
was *»<rrtaine<i that the reflected light occupied alxmt !(>' JO'
in traversing the earth’s orbit, and it may be slated in round
numbers that the velocity of light is about equal to 21H),(KH)
miles per second, or more precisely 106,072 geographical miles,
a velocity almost n milium times greater than that of sound.
Such a velocity seems beyond human comprehension ; and yet
the Astronomer, by pursuing the practical course of observa-
tion, lias succeeded m measuring distances so vast that they
permit the velocity of light to be used a» an element in their
expression. It is thus that the light of some of the fixed stars,
whose' distances have been determined, must have taken 5, 9J,
ami 12 years to travel to the earth; or supposing the whole
universe to liavc been contemporaneously created, 3, 9], and 12
years must have elapsed before those stars respectively could
have been perceived on the earth ; and were they now to be
annihilated, the same periods must elapse before they will cease
to be visible. There may indeed be heavenly bodies the light of
which has not yet arrived at our terrestrial surface, and others
may have been annihilated, although they yet appear to shine
upon us ; and we may therefore well say with Humboldt, that
“ whilst we penetrate with our large telescopes at once into
space and time, and measure the one by the other, we may

RttDIMKNTAftY GXOLOQY.

5

r ram the nrt of light which come to os as if they were
voices telling of the past ; and however much we may diminish
both the supposed distance whence the faint light of the ncbuhe
or the barely discernible glimmer of the remotest clutter of
stars reaches us, —and the thousands of years which serre at
the measure in time of that distance, — it will still remain
true that, according to the knowledge which we possess of
the velocity of light, it is more than proliablc that the light of
the most distant cosmical bodies offrrs us the oldest sensible
evidence of the existence of matter.** And is not this s most
important testimony for the Geologist ; for when he too is
obliged to sjieak of vast periods of time, may be not fipfeal to
the Astronomer for proof, that the first act of creative power
was exercised at an ejioch so remote, that even the mighty
velocity of light, and the vast distances of the celestial bodies,
are inadequate as measures to express it f

The other phenomena of light, as its refraction, its double
refraction, and its |*da rotation, — those remarkable effects pro-
duced on light in its passage through crystalline bodies and
by which their internal constitution may lie examined,—
might Ik* also adduced as results of a happy union of the
practical and theoretical, or, in other words, the observing
ami reasoning systems. It is indeed by a knowledge first
acquired by induction from facts observed, and to the me-
chanical skill applied in aid of it, that the refracting teieaco|»e,
and, by a similar knowledge of the laws of reflection of light,
the reflecting telescope, have been so perfected as to open to
our view an infinity of worlds and to track the very steps of
their creation ; whilst the achromatic microscope has been
made to reveal to our gaze an infinity of minuteness equally
wonderful, and to teach us the wonderful truth, that some of
the solid rocks of our world are hut an accumulation of count-
less myriads of minute organic bodies. Such intellectual
triumphs ss these demand on our part a tribute of admiration,
not merely to the exalted genius which seizes on the laws
which connect together great physical phenomena, but to the

G

RUDIMENTARY GEOLOGY.

practical man who, as a patient, careful, and acute observer,
diligently watches for (acts, or subsequently submits the theory
established on them to the test of experiment.

Let us compare the ancient Mariner, cautiously pursuing
his course along the shore and watching the declining star,
with the skilful Voyager of the present time, who boldly quits
the land, and securely steers over the expanse of ocean,
the heavens affording him also a guiding -light for his ad-
venturous progress ; and how great a difference will appear
net ween the mere perception by the one of a regularity in the
movements of the celestial IkmIics, and that accurate knowledge
of the distances and motions of the various heamily bodies
which has enabled the AstrmHimcr to supply the modern
Sailor with tables and formula- by which he determines from
celestial observations his exact {xnitton and move* as securely
upon ocean as upon land. And on the land itself, where the
druse forest clothes the surface and forbids the ordinary
operation* of the Surveyor, recourse can Ik* bad to celestial
observations, a* was recently done in the determination of our
North* Eastern American boundary by the Surveyors, Officers
of the Corps of It oral Engineers, who having first determined
the latitudes and longitude* of the end* of n line of till miles,
deduct'd the azimuth or bearing of cadi end from the other,
and then proceeded to cut down the tret** according to these
lienrings, beginning simultaneously at each end, aud so pur-
suing the respective lines through (lie forest until they both
nearly met, the two {tarries emerging not indeed exactly
opjKtmite to, l>ut in dost* proximity to, each other.

Astronomy, therefore, both in its marine ami its terrestrial
applications, affords the most powerful proofs of the advan-
tage of never separating practice from theory , of considering
the observer or the practical Astronomer as the fellow-
labourer of the Theorist, and at the same time of frankly
acknowledging the benefit* derived from the profound investi-
gations of the latter. M. Biot has stated his optmoo that
the only safe method of arriving at knowledge it by indoo*

ItDlXlNTAftY GEOLOGY.

7

tioo. " When observations Harp accumulated, they art com-
pared together, and their errors discovered and eliminated.
A correct knowledge is thus acquired of the state of the
heavens, as to what is constant and what is variable, whether
it be in a day, in a year, or in tome still greater interval of
time. Tilt* task of observing, on Practical Astronomy, ceaacs,
and that of Theoretic Astronomy commences. Similar phe-
nomena are comjwtrrd together, in order to discover the law*
by which they art* linked together; and then again the inquiry
is extended until the movements of the heavenly bodies hove
been shown to be in harmony with those mechanical forces and
those laws of attraction which are found to operate upon all
material bodies.”

Chemistry is replete w ith illustrations of the principle which
these remarks inculcate : it is an experimental science in the
highest degree, and at every step of it* progress apjieals for
information to the crucible and ha lance. And yet, though a
practical science, it is rich in deductions of the highest philo-
sophical interest which spring from the exercise of jiowcrful
reasoning ii|wm carefully observed facts. Thousands had
observed the phenomena of Ixwlic* falling to the ground
before they stiggestifi to the miml of a philosopher the laws
of universal gravitation ; and many a patient Chemist had
weighed the resulting constituent* of bis careful analyses, err
the miml of Higgins obtained a glimpse, and that of Dalton a
clear perception, of the remarkable law of definite proportions,
by the discovery of which Chemistry w«» at once raised to the
rank of an exact science. This law has now bceorne so
familiar that its beauty and grandeur are Dst considered than
its convenience ; altlimigb it may he doubted whether in the
whole range of science any greater discovery was ever made
than that which established the fart, that the combinations of
material substance* are neither arbitrary in kind nor quantity,
but determiner! and limited by definite and invariable laws.
The atomic theory of Dalton is a philosophic or theoretic
expression of this fact ; but whatever may be the fate of the

the constitution of minerals, ami on their variation within cer-
tain limit* by a Kuhstitution of similarly constituted elements,
one for the other, it has placed Mineralogy on a sound basis.
Nor hate the economic lesson* of Chemistry been less im-
portant : in Agriculture, hy showing the true constitution of
various plants, they have established the 'nine of inorganic
as well as organic manures, and prosed that the soil cease*
to he productive from the exhaustion either of the mineral
or the organic elements necessary for the growth of the
plant; — they have shown alio that the carbon of plants
is principally obtained by the direct action of the leaves of
the plant on the atmosphere , — the) have discovered iu vege-
tables many of the principles which wire *up|>osed to belong
exclusively to animals, and {minted out a most singular
analogy betwern the function* of both : ** in plants,” says
Dumas, *• the fruit, or rather the grain, is rich iu fatty matter
which is destined to produce heat by its combustiou during
germination ; in animals the fat is also kept in reserve to he
used for combustion iu respiration, should the supply of
nourishment fall short. There is reason to believe that the
fatty matters originate in the leaves, and are thence carried to
the embry o to be deposited either around it, or in the seed
generally. These fatty matters pass into herbivorous animals,
and from them into the carnivora, so that the supporter of
combustion in the vegetable seed and in herbivorous and car-
nivorous animals has been elaborated in the green leave* of
plants facta which may well excite the admiration of th*

RUDYMEKTARY GEOLOGY. %

scientific and command the respect of the practical man ; and
it la by such lessons that the practical man is enabled to
understand why he obtains successive crops of some plants
from the same ground, as the Botanist finds a plant on the
vetT spot where it hss flourished for ages, although his com
crops, by taking away from the ground the necessary in-
organic elements, quickly render \t unfitted for their continued
growth. Chemistry goes hand-in-hand with Geology in this
important practical application, and the Farmer is beginning
to cast off Ins ancient prejudice, and to hail, as most uaefiil
auxiliaries, sciences which not merely indicate to him the
ealuable qualities of the various mineral substances which
enter into the vegetable structure, hut even direct him where
they are to lie found.

The practical man is however aware that in any occupation
of life no theory ran supply the plan* of practical skill; ami
the consciousness of the necessity of such skill too often
induces him to overlook the fart, that skill was originally set
in motion by science, and that what is sometimes called a
lost art, ought in reality to lie styled a lost science. It is
thus that many processes of a very ordinary character, »urh
as those so long adopted in the manufacture of white lead, a
pigment known to the Ancients, involve principles of high
scientific interest, which must hare been perceived, however
obscurely, by their first originators.

The beauty and excellence of church glass during the medi-
eval ages were probably the consequence of scientific know*
ledge in some of those early student# of Nature, the Monks ;
and if the art is now reviving, am! promises ere long to rival
its former condition, the improvement should he ascribed to
science applied tn aid of practical skill. Such examples might
be multiplied from the pr o ce s se s of bleaching, dyeing, distill-
ing, and of Metallurgy ; and even more strikingly from the
application of electric and electro-magnetic' science to the
galrano-plastic processes and to the telegraph ; all tending to
demonstrate that whilst the only sure basis on which any

10

»HG D1 M ENTS UY GEOLOGY.

science can be founded is the olnervatioti of fads, or, to other
words, practical inquiry, so also the sure basis of every art is
science. When, however, an art lias been founded on a sound
knowledge of principles or laws, practical skill may, by the
tact it acquire*, greatly improve and advance it, and an art
may be even perpetuated in live hands of those who have for*
gotten, or perhaps have never\uown tlie science go which it de-
pends ; and it is thus tliat, in some refined art which has come
down to us from a remote ej>och, we may often read a record of
scientific labours which have left no other trace behind them.

The characteristic of the present age U jJ»c continued effort
to trace every practical residt up to a scientific principle, and
to seek in that know ledge of principle* a power to modify
or extend results. The truly wonderful devclopinent of all
branches of our manufactures , the extending application of
machinery' in aid of human labour of cu*ry description; the
state of our communications by sea aud land under the im-
pulse of steam power ; the application of magnetics! and
electrical science to so many practical objects ; each, and ail
of these, testify to this one great axiom, that permanent im-
provement can he founded on knowledge only. Before the
light of science scen ts disappear or become principles. It is
thus that the French Chemists, MM. KUlmeu and Salyetat,
have devoted themselves to an inquiry into the composition of
the materials used by the Chinese in the fabrication and
decoration of porcelain, and having completed their cliemical
analysis, have already commenced experiments at Sevres, in
order to reproduce in that manufacture the colours of the
v Chinese artists. But there is perhaps no more striking ex-
ample of the power of science to dispel mystery than is to be
found in the researches of M. Boutigny DXvreux. That in-
genious philosopher has ascertained that the old miraekw of
the ancient priests of Zoroaster, and the equally wonderful
examples of the v successful issue of the ordeal by five in tha
medisvnd ages, are explicable on sound physical principles,
and has tested the accuracy of his reasoning by plunging

RUDtMKHTAEV GKOUK1I. U

without injury liis hand into hath* of molten metal*. Tin*
remarkable phenomenon he explain* by assuming a new force,
namely, the repulsive power of caloric at sensible distance*
acting on liquids in what he calls the aplieroidal state ; hut
to the explanation strong objections have been urged, and
M. Person considers it unnecessary to seek any new cause*, and
ascribes the result to the tension of a him uf vapour which is
suddenly formed between the heating body and the liquid and
keeps them separate. If, for example, the hand he cither
naturally or artificially moist, there will be produced on it*
approach to the melted metal a film of vapour which will, by
its tension, rcjH?l the metal from the hand, and for a time
preserve it from injury ; or if the hand l»e dipped into ether,
and then into boiling water, there will be a coating of vaj>our
of etlier formed on the hand, which will repel the boiling
water and preserve the hand from scaldiug. In all these cases
only part of the protecting fluid is reduced to vapour, and there
is between the vapour ami the hand a coating of the fluid, w hich
being a bad conductor of heat, further insures safety; the only
precaution necessary luring that of selecting for tlie protecting
fluid one in which the vaporising temperature is considerably
below that of the melted metal or of the boiling water.

In no science has the value of inductive reasoning been
more strikingly illustrated than in Geology, which is the more
immediate object of this volume ; nor lias any more strongly
proved the importance of the sound knowledge thus acquired
in advancing the practical interests of ynanktod. Glimpses
of the formative and modifying functions exercised by both
fire and water were assuredly obtained by the Ancients ; fof
it was impossible that thinking bud could contemplate the
action of men and of the sea in wearing, transporting, and
depositing the mineral matter of the earth** surface, or that
they could watch the glowing flood of melted lava, as it
poured from the volcanic crater, without recognising the
power of those great agenda*. To them, however, the labour
of collecting fleets was dieCastefel, and the passion of s pecula*

13

KGD1MKKTAKY GKO LOGY.

tire theorising was so strong, that whilst they played with the
dreamy hypotheses of possibilities, by turns advancing to or
receding from the truth and sometimes even anticipating dis-
covery bv conjecture, they never succeeded in establishing a
correct theory of the formation of the earth. So long indeed did
this spirit of speculation continue to maintain its influence, that
the Haro man system of inductive reasoning only slowly made
its way in Geolog)' ; and the positive evidence of the senses
was rejected id the rase of fossil organic bodies, or the
remains of ancient and no longer existing animals found
imbedded in the stonv masses of the earth's strata, and it
was attempted to explain their existence by a hypothetic
plastic power in Nature which liad been exercised in forming
so many Iumhm nature. It would l»c useless to enumerate all
the great men alio have aided m dispelling the obscurity con-
sequent on mere scholastic discussion by appealing to an ob-
servation of facts. In doing so tliev pursued two leading
courses: the one, an examination of the mineral matter of the
earth's surface, with a view to determine the actual manner in
which it had breu arranged ; the other, an investigation of the
nature and history of those vestiges of a mauds and vegetables,
which, being found hi the iuleriur of mineral masses, prove
that a portion, at least, of the crust of the globe lias been
formed subsequently Ui the existence of organic beiugs.
Lehmann, in 176b, made the first satisfactory step towards a
correct knowledge in the muicrai inquiry » bj his description
fif the stratified drpqpits (FUeUgebirgrj of the ceutre of Ger-
many. Subsequent Geologists pursued the same course of
Careful observation, amongst whom may be specially noted
the illustrious Saussure; and at the dose of the last cen-
tury, Werner gave new impetus to the science by gene-
ralising the results of his own observations, and arranging
them into a system. It was to be expected that the peculiar
district or held of inquiry would influence materially the
deductions of the fir* observers ; and that whilst W erner
built up an aqueous theory, in which he suppoacd all mineral

RUDIMENTARY GEOLOGY.

13

matter to be deposited from a solvent fluid, Ilall, having de*
rived hit knowledge of the action of highly heated masses firom
the examination of a totally different country, established an
igneous theory ; and that modern Geologists, proceeding
on the principles so ahlv set forth by Sir Charles Lyell,
who may l*e considered the founder of our present system
of geological reasoning, would liesitatc to reject any cause
which can be now observed in the operations of Nature, and
would carefully combine together in one great system all
those forces which, whether nqucous, aerial, or igneous,
now act on the earth’s surface, and judging from thr simi-
larity of effects so palf table in the ancient strata, have also
acted at all former periods within the reach of our observa-
tion. In the second branch of inquiry the progress was
even slower ; for though, in l 1 7, Fraacatoro had remarked
tliat all the organic fossils then discovered could not have
been buried at the same epoch, anti Stciiou, in I fib!), had
hinted that they might Ik* used to distinguish the relative
ages of the masse* containing them, the prejudice to he over-
come was so strong, that l\tla*< m t oh >gy can scarcely be said to
have become a recogimcd branch of geological science until
William Smith announced, in 1 7*10, thr design of piihlisliing
a geological map of (treat Britain, which he effected in iHi/i,
and thus promulgated the fact, that England is constituted of
strata the superposition of which is constant and never in*
verted, and that the same fossils being found in all parts of
the same bed, it may be characterised by those fossils. The
genius of Goner shed s new sod brilliant light over Pabron*
toiogy by establishing the laws of anatomical composition, and
building up in conformity with them the remains of the higher
animals, so as to exhibit to the Naturalist many remarkable
forms which, though they base ceased to exist, are connecting
links in (be great chain of the animal kingdom. Many are
the great mro who have continued to work out, with unceasing
labour, this great subject ; and it is no small gratification to
know that Grecoougb, Rockland, Sir H. He la Beebe, LyaU,

14

mUPfMSKTA&T GEOLOGY.

Sedgewick, Conybearc, Fitton, Phillips, Murchison, are still
living amongst us, and by their inquiries and their reasonings,
adding new lustre to a science which hat, as it were, grown
up under their care and guidance. Geology, therefore, is now
a true science, being founded on facts and reduced to the
dominion of definite laws, and in consequence has become a
sure guide to the practical rntfn : the Miner finds in it a torch
to guide him, in his subterranean passage, to the stratum
where he msy expect to fmd coal or iron, or to the recovery
of the mineral vein which he has suddenly lost ; — the Engineer
is guided bv it in tracing out his roads or canals, as it tells
him at once (lie firmest stratum for supporting the one, and
the easiest to cut through for tlie other, and makes him
acquainted with the qualities of the materials he should use
in his const ruction*, and the localities where he should seek
them; — the Geographer finds his inquiries facilitated by learn-
ing from Geology the influence of the mineral masses on the
form aud magnitude of the mountains ami valleys, and on the
course of rivers; — the Agriculturist is taught the influence of
the mineral strata on vegetable and animal life, and the States-
man discovers ui the effects of that iufluiMice a force which
stimulates or retards jxvpulation ; — the Soldier also may find
in Geology a most valuable guide in tracing his lines both of
attack and defence , — and it is thus that a science rich iu the
highest objects of philosophical r<**earcb is at the same time
ca{iablc of tlte widest and most practical application.

Can it be doubted, then, that there ought to Ur an intimate
unkm between practical and theoretic men, — between the
observer aud the philosopher? — tad is it not also evident that
the position of the practical man is often most favourable for
the collection of facts which be overlooks only because bis
mind has not been trained to observe ? When the most simple
practical man has observed a fact, to that extent, be has ac-
quired knowledge and become scientific ; and though he over*
look* many other facts, he has often stored up more knowledge
than is supposed by the theorist. To extend his powers of

rudimentary geology*

15

observation is the object of this volume, and it k believed that
every applied science will acquire additional extension and sta-
bility by availing itself of the quiet labours and sound sense
of practical men.

chapter ii.

Gkoloot— I ts Meaning, Object, and Utility as a Science.

Geology, a treatise or discourse on the Earth, is a term
which admits of a very wide interpretation, and naturally
suggests to the mind inquiries— 1st, into the formation and
original condition of the earth ; 2ndlv, into the successive modi-
fications which it has undergone, and the agencies by which
they have been effected ; and 3rdlv, into its present condition,
and the agencies w hich arc still product ng changes in that con-
dition. The first object, thru, of the Geologist is to establish,
on the principles of inductive reasoning set forth in the in-
troductory chapter, the science as it depends on each of
these inquiries, and then to apply it to the practical pur-
po*e» of life : and it may be premised that a science it
practically valuable just in proportion as its facts have been
discovered, and its laws established and studied, for so long
as we an* uncertain whether a known result has proceeded
from a defiuite cause, wc are unable to apply the fact or cir-
cumstance to the elucidation of other facts or circumstances,
and so kmg as we are unacquainted with the properties of any
substance under onr examination, we cannot declare with cer-
tainty what share it mny have had iu the phenomena we bare
observed. This may be illustrated by a reference to gun-
powder: its explore quality is the result of its composition,
and we can only depend upon the results when we know that
the compound has hem accurately formed : to insure, therefore,
certainty in the operations depending on it, we must take cure
that a proper standard of composition has been adhered to,
1 a a similar manner, wt can only apply Geology aa a practical

16

mrWMENTAKY GEOLOGY.

science when we have ascertained and made ourselves familiar
with those facts which prove the first principles on which it
has been founded to he correct and stable.

To obtain any idea of the earth* s formation and original
condition, we must treat Geology as a branch of the physical
science^. The earth, as one of the planetary bodies revolving
round the centre of our solaf system, must, like all the other
planets, be subject to the great laws by which they are at N
once retained in their orhits and caused to revolve on their
axes ; it is only one member of a great whole, and in its density,
its volume, and its mass, is in strict relation to all the other
bodies of the same system. The first formation, therefore, of
the earth, or the manner in which it was probably condensed
fVom nebulous matter, and reduced to the planetary form, may
he considered a portion of Astronomical science.

It is thus that Astronomy has assisted in the determination
of the form of the earth, and it is now known to lx* an oblate
spheroid, of which the equatorial diameter exceeds the polar
by HO. 2% feet, or alxiut 20 geographical miles, — a difference
equal to more than nine times the height of Mont Blanc, or
fire times thr bright of the highest point of the Himalaya
chain. And in like mnnnrr. by referring to the laws of matter
as exhibited in gravitation and attraction, the Philosopher has
been enabled to weigh the earth he had Ixforr measured, and
has determined its mean density to be about . f »J times that of
distilled water : hut as the actual mean density of the solid
matter of the earth** surface, its rocks and strata, does not
exered 2*D, there must lx an increase of density from the
surface to the centre of the earth. It is impossible that
man should descend so low into the interior of the earth
as to discover from within the actual condition and nature
of its mineral masses, hut he has, at least, obtained from
without some due to it in the falling aerolite, or meteoric
atone, — the elementary identity of which with the matter
of our earth, — the presence amongst it* constituent* of
the mineral aogite, which b an essential ingredient of sub-

RUDIMENTARY GEOLOGY.

17

aqueous volcanic products, — the unoxydixed condition of its
iron, which indicates that it had not been exposed to atmo-
spheric agency, and its high specific gravity 3*575, that of
the iron itself being 7*713, — are illustrations of the internal
constitution of our own planet, ami of n general harmony in
its mineral matter and that of the other planetary bodies. In
other stages of the subject there will be frequently occasion to
refer to general physical laws ; but if wc turn for the present
to the more practical investigation of the past and present
state of the earth’s surface, we shall soon be convinced that
there is something more in its rocks and strata than mere
masses of stone, or heaps of gravel, sand, and mud, confusedly
thrown together: we shall find, in fact, that these deposits
have Wen the result of forces tending, according to the ordi-
nary laws of nature, either to break up and remove, or to
dc|K)*it And consolidate in new forms the mineral strata,
and that Geology is thus connected with the experimental
sciences of Meteorology and Chemistry: nor is this all ; for
whilst wc examine the mud and sands of our own coasts and
stas, and find either imlxvldcd in, or resting upm them, the
relics of many living sjiccir* of animals and plants, we cannot
overlook the analogy m distribution ami arrangement ex-
hibited by the sandstones and clays ot other epochs, and the
wonderful fact that they too arc associated with the relic* of
organic beings: we Irani indeed the close connection of
Geology with all the natural sciences, and are taught to view
it not merely as an humble invrstigaumi of the circumstances
of inert matter, but as a lofty exj>osii»on of the mysteries of
organic creation.

Enough lias hero said to impress upon the reader the phi-
losophical importance and dignity of Geology ; snd it can he
easily shown that its practical importance is the result of
its philosophical connection with the exact sciences. For
example, were all the deposits we meet with, here rock and
there sand, gravel, and clay, mere arbitrary heaps which had
never been brought under the controlling influences of organic

|g KVDIKKNTAftY GEOLOGY.

or inorganic forces, we should be unable to use the one as
an indrx to the history of tlie other, and the study of each
tndividiiai deposit would end as it had begun, in itself alone.
But if it be proved that certain physical agencies have, ac-
cording to fixed laws, been in operation from the earliest
periods of our planet's history, and that they have cither
co-operated with, or acted upon, organic Wings, so as to check,
modify, or destroy, at successive epochs, animal and vegetable
fife, — and if in the strata themselves we can find the fos-
silized rtdics of successive races of organized tieings, and can
make the one a guide to the other, — how different is the re-
•ult, uncertainty now giving place to certainty, and a know-
ledge of the strata of one jiortionof the earth's crust liccoming
a clue to the investigation of the strata of any other. It is
upon t lua certainty, obtained by the collection and collocation
of facts from all |iart» of the world, that Geology rest* ita
claim on the attention of practical men.

In order to acquire a clear conception of geological phe-
nomena, it is necessary to take a brief review — 1st, of the
various elementary substances which enter largely into the
composition of the earth s crust, and of the fluids connected
with it ; and 2ndly , of the principal compounds formed by
them.

Including most of the metals, there are more than fifty
substances which, having hitherto resisted the effort* of the
Clicuust, are at ill considered simple. Of these, sixteen only
occur extensively amougst ordinary mineral comjiounds, whe-
ther fluid or solid ; they are, orggen, hydrogen, azote or nitro-
gen, carhim , sulphur, chlorine, Jfuonne , phosphorus , siUmum ,
aluminium, potassium, sodium, magnesium, calcium, iron, and
manga nest, which, combined together in various ways, com-
pose the greater portion of the earth's crust and of its teas
and atmosphere. Some of the other elementary substances, as
bromine, iodine, ami bonne, are highly interesting, and tome,
as the metals, are moat important ; and though they do not
constitute so large a portion of the whole as to require a

rudimentary geology.

19

specific notice in this part of our subject) the remarkable ex-
tension of some of them throughout nature deserves remark,
as is especially the case with iodine, which will be therefore
included iu the list of Geological elemeuts.

The important offices of some of these substances are gene-
rally known ; as for example, of hydrogen and oxygen in
water, — of oxygen and nitrogen in air, — of carbon as a minute
but very essential constituent of air, — of carbon again as a
combustible substance in turf', wood, ami coal, — of iron as the
most useful of metals ; but in addition to these well-known
offices, they have others, which are little less essential and
marked, to perform in the mineral constitution of the earth's
crust, the minerals of which it consists being principally formed
by the combination of some of these elements with the prin-
cipal metallic bases; a fait which will become evident at we
consider them in order.

Oxygen combine# with siheiurn to form silica, of which it
constitutes more than a half; hut silica, either purr, or com-
bined as ati and with metallic banes, has been estimated to
form almost one- half of the solid crust of the terrestrial globe ;
and hence oxvgru, iu tins one condition, is equivalent to a
quarter of the ponderable matter of the earth's surface. Hut
oxygeu is also combined with alumiuium to form alumina,
an earth wluch is an essential constituent of certain minerals
and rocks, as mica and clay slates, Ac., which extend over large
tracts of the earth s surface and produce by their decomposi-
tion the beds of clay, so general throughout the world, — the
several ram ties of clay being essentially silicates of alumina
proceeding fiotu the decomposition of the felspar and mica of
granite, gneiss, mica slate, and day slate,— ami when the
quantity of mud or clay found in modem alluvium and the
beds of day in more ancient deposits are considered, the im-
portance of alumina is only second to that of silica ; but of
this earth, oxygen m weight forms nearly one-half Again,
oxygen forms oearh one-half of carbonate of lime, the basis of
limestone, a mineral of which, in many part* of tlie world.

20 BUDIMEKTABY GEOLOGY.

mountain masse* of many hundreds of feet thickness are con-
stituted. And if we add to these instances its presence in
water, which is so abundant in the mineral as well as the
vegetable and animal kingdoms, and of which it forms in
weight eight-ninths, we may readily lielieve that of the whole
crust of the earth, at least* one-half is cotnjiosed of this re-
markable element.

Hydrogen, as a constituent of water, enters into the com-
position of many minerals and mineral strata, and forms a part
of almost every organic substance.

Asotr or m tn*ren, as a constituent of the atmosphere, of
most animal and of several vegetable substances, i* an im-
portant element, although it is scarcely appreciable in the
mineral kingdom. Tract's of this fundamental element of
animal organization are, however, to be observed, in the form
of ammonia which is a compound of nitrogen and hydrogen,
in strata which contain the fossilized remains of animals, and
such traces have hern apj**nled to as a test of the former
presence of animals in strata which now exhibit no fossil
evidence of their existence ; hut however striking this exhibi-
tion of ammonia max be. it is subject to so many sources of
uncertainty as to Iwr justly considered insufficient in deciding
ao obscure ami difficult a rpirstion. One of its roni|>oiiiids,
nitre or saltpetre, nitrate of |»ota«h, is well known as a con-
stituent of guujHiwder : it is produced naturally and is found
efflorescing on old walls. In India it is so abundant as to
crystallize on the surface of the soil. The analogous salt,
nitrate of s*nla, occurs in Peru in a bed several feet thick, and
extending oxer a sjiace of more thau 40 league*.

CarUm, the liasis of coal, the liase of carbouic arid, and the
most considerable element of the solid part* of animal* ami
vegetables, is one of the most important substance* in nature ;
it form* nearly one-eighth part of carbonate of lime, and is
therefore an essential constituent of the earth** cru*t. In its
purest form it constitutes the diamond, at once the hardest and
snoat brilliant of gems.

RUDIMENTARY GEOLOGY.

21

Sulphur, a constituent of animal and vegetable substances,
is exhaled in large quantities from many volcanoes, either in a
pure state or in combination with hydrogen, and lias probably
proceeded from some of the mineral substances with which
they* are connected or has been sublimed from deeply seated
beds of sulphur by volcauic beak It is also a part of the
mineral crust of the earth, as it occurs in the sulphurvts of
the metals, and in sulphate of lime or gypsum. As regards
the sulphurets, its presence is sometimes secondary, being the
result of the juirtiid decomposition of the sulphuric acid of
soluble sulphates in a singular chain of compositions and de*
comjKisitions. In beds of shale, iron pyrites (bisulphurct of
iron) is frequently very abundant, and when water gains access
to it, there is a partial decomposition, some of the oxygen of
tlu* water combining with the sulphur to form sulphuric acid,
wliieh then combines with the iron, also nvidi/cd from the
water, to form sulphate of iron. The soluble sulphate i% carried
away bv the tilt* ring water, and when it comes m contact with
Ajuuml or vegetable substances imbedded in the strata, is again
decoin|M>sed, the oxygen eomhmiug with the hydrogen and
carbon of the organic IxhIic* to form water, carbonic acid, and
carburetted hydrogen, and a sulphuret of iron being deposited
in their tissues. The results of this process* as exhibited in
fossil v egr tables and in the organic portions of shells ami
fish, are sometimes very beautiful, and it may be conjectured
that this succession of coui|H»sitions and decompositions will
xet Ik* traced up to an earlier commencement mi the morn
ancient geological strata.

M. t‘h. lUondrau has rceeutly discovered tiiat sulphuret ot
arsenic exists, in solution, in oil powerful mineral springs or
waters, ami he ascribes tlieir medumai effects to its presence.
Sulphurets of iron and ot v anrse are also found in thermal
waters.

Chlorine, as a constituent of chloride of sodium (common
•alt), takes part in the formation of those extensive beds 0/
lock salt which occur in various geological formations. Ohio*

22

*roiH*?tTA«T GEOLOGY.

line forms nearly of chloride of sodium, and is therefore
another example of a gaseous body entering extensively into
the composition of the earth’s mist. 1'nited with hydrogen
as hydro-chloric acid, it is evolved from voleanocn.

Ft murine, when combined with nxygrn as fluoric acid, unites
with lime to form fluatr of time, or floor spar, which is often
associated with lead in win-stone*. It is also a constituent of
mica and hornblende, hut it may !>c considered important
rather in a mirirralogical than p*ol<>gicaI sense.

Iodine is well known ns n jw>wrrful medicinal ngem. Com-
bined with the base* of potash, soda, and magnesia, it co-
exists with common *a!t in sea. water and in marine plants.
It ha* also been recently proved by M Chat in that it exists
in fresh water plants, in the waters af nvpm, springs, and
wells, and in the structure of atpiatie animals, so that it is
evident that this siihatance, only discovered in 1*1 I, i* widely
spread over the surface of the earth, and doubtless forms a
part of its internal mass. It has also been found in coal ; and
M. Chatin has deduced from the greater or lew amount it
the several varieties of roal. Anthracite and Lignite, an argu-
ment for ascribing their origin either entirely to cryptognmic
aqueous plants, to a combination of arjueou* and tcimtrud,
or chiefly to terrestrial plants, as the particular ease may be.
Iodine ha* been found combined with silver as an iodide of
silver in Mexico.

Bromine also occurs in sea water combined with the base of
magueaia, and lias also been found in salt springs.

Bonne combines with oxygen to form boraric arid ; and the
salt borax or borate of soda is formed naturally on the toil
in Thibet, and is found also at the bottom of certain lakes.
Boraric arid occurs in the crater of Volcano, one of the Ltpari
Islands, and is emitted from the earth in combtnatkm with
hot vapours in Tuscany: it is a constituent of the mineral
tourmaline, which contains about 8 per cent, of boraric arid,
and tbs wide distribution of tint mineral, estimated by number
of localities and not by quantity, co mb ine d with the vol can ic

RV DIM* XT ary gkolocy. 23

origin of the acid, proves that bonne mutt hart formed part
of the original matt of the earth.

Pkotpkor **. — A constituent of phosphate of!i»tu\ which it,
at Apatite, rather rare in the mineral Kingdom, hut is a moat
important compound in the animal kingdom, being the mineral
portion of hone, the strength and stability of which depend
upon it. It is also a constituent of nmnv vegetables, and
enter* from them into the animat *trurt*re . l>arwtn men-
\ *ns two curious secondary production* of phosphate of
lime, ■ -one at St l*nut*s Islands, where the rocks are coated
with it. tbr act mn of the sprue on the dung of sea-fowl
hating produced phosphoric and , anti nt Ascension, where
stalactites of the Mime mineral have been produced in a similar
w .in

Siiictnm or Silicon, the metallic basis of silica . — - * Tlie
important position this substance occupies has been shown
under * Owt-en most of (he minerals, exclusive of the rar-
Ixiontrs and sulphates of lime which form the earth’s crust,
appearing in the form either of silei or of silicates The
water of springs and wells always contains a little soluble
silira : in mineral water* its quantity is sometimes more eon-
siderahlc, and associated with an Alkaline carbonate, it occur*
in the hot alkaline spring of Ilrikum, in Ireland, and in th©
boiling jets of the Geyser. These latter modes of occurrence
indicate the alow but continued destruction of the silicate* of
Jhe mineral kingdom, and afford a probable explanation of the
formation of much of the crystalline quart* in nature ; on the
solution of many limestones gelatinous ailtea is found, and its
pmenrt indicates that s similar process was connected with
their formation.

Jluwtimum , the metallic base of the earth alumina. — Alu-
mina, as one of the principal constituents of day, and of all
those minerals and rocks from the decomposition of which it
te produced, is, as shown tmdrr 4 Oxygen/ a most important
portion of the earth's crust. It is also well known as on a of
the component parte of elans, e salt extensively need in dyeing.

34

KriMMEKTARY CEO LOOT.

which i> A double sulphate of potash and alumina. The sul-
phate of alumina is formed naturally by the action of sulphuric
acid, proceeding, as already stated, from the decomposition
of iron pyrites, on the beds of clay or of shale in which that
mineral is abundant. The sulphate of alumina being dissolved
out, and separated by crystallization from the proto- sulphate of
iron formed at the same time, is mixed with sulphate of
potash, and the two combine to form the double salt alum.
Alum-stone, a natural product of volcanic countries, also yields,
by heating, this substance : it is abundant in the ancient
crater of Rolfatara, near Naples. Though alumina is the
principal ingredient of plastic clays, it forms nearly 99 parts
out of lOt) of the beautiful gem sapphire, next to the diamond
in hardness,

Potatnum, the metallic base of the alkali potash. — Potash
is a romjKment of many minerals, c»|x*ci*lly of felspar (a well-
known constituent of granite and gneiss), of which, in the
condition of a silicate, it forms nearly |th part. The soil is
provided with the jKitash necessary for the support of various
plants from the dcrom posit ion of rocks containing felspar ;
and being again extracted from these plants to lie used in the
art*, it ha* obtained the name of vegetable alkali. It i* the
haae of the important mineral eom}K>wid, nitre or uitrate of
potash .

Swhum , the metallic base of soda, an alkali which replaces
potash in albite (sc* la felspar). — Soda has been called the
mineral alkali, in contradistinction to potash ; but such dis-
tinction is without foundation, as carbonate of soda is obtained
fVom kelp, or the ashes of calcined set-weeds, and might
therefore, as a secondary product, he also called vegetable.
Soda is likewise found in all animal fluids, and the haae itself
is widely diffused in that most valuable salt, the chloride of
sodium, or common salt. The importance of sodium as ooe
of the constituents of the mass of the earth will he under-
stood better by estimating the quantity of suit in sea- water
than that in beds of rock aalt, however extensive. Chloride

mVDlMKNTAlLY GEOLOGY.

25

of sodium forms about the ^th part by weight, or about ^ th
part by bulk, of sea water, and the bulk of the sea being about
y-fjth of that of the whole earth, the quantity of salt it
contains is about psrt of the whole earth, or about

^tyth part of the bulk of the actually protruding or dry
land. If it be considered probable that the saline condition of
the sea is only the result of the long-con turned action of water
upon the solid mass of the earth, there will appear to be good
reason for assuming with some philosophers that sodium,
potassium, and other metallic bases were important original
constituents of the nucleus of the earth, and that by their
sudden combination with chlorine and other gases they pro-
duced some at least of the convulsive disturbances of its crust.
Nitrate of soda abotihds in Peru.

Maynetium, the metallic base of the earth magnesia. —
Magnesia, as a silicate, is a component of many important
mineral*, esj^cially of pyroxrne or augite, of amphtlxdt or
hornblende, of steatite, ami of serpentine. Of hornblende it
forms 1 th j»art. It is also remarkable as a constituent of dolo-
mite, or magnesian limestone, a combination of the carbonates
of lime and magnesia which is very extensively diffused in
nature, and forms occasionally mountain masses. The effect
of magnesia on vegetation is well known. Asa carbonate, it
would in itself perhaps he innocuous, but as it forms on decom-
position very soluble salts, it may be carried into the vegetable
organism, and thereby prove injurious. As an alkaline earth
it is dangerous from continuing so long in a caustic state.

Calcium^ the metallic base of the earth lime which forms
more than a half of carbonate of lime. — it is unnecessary to
dwell on the vast importance of the Utter mineral, both as an
economical substance and as a constituent of the earth’s crust ;
but lime is also found as a component of another valuable
mineral — sulphate of lime, or gypsum, of which it forms about
|th part. Gypsum occurs in extensive beds in more than one
geological formation ; in America in the primary or Silurian,
fat EngUiwl god Ireland in the secondary, and dong the l&edi*

26

RUDIMENTARY GEOLOGY.

terrmneen n> the tertiary strata, divisions which will be here-
«lter explained. Lime also enters into the composition of a
great variety of minerals.

Iron . — The mere name of this metal must recall to memory
the multitude of uses to which it is applied, and justify us in
regarding it as one of the greatest gifts of creative intelligence
to man. In addition, however, to its occurrence in a mineral
state in our coal measures, as clay iron-stone and also as
spathic iron, both of which are carbonates of iron; in masses
and in disseminated nodules as anhydrous and hydrated per-
oxide of iron, or red and brown hematite ; in the magnetic
oxide and h» specular iron, or Elba iron, — minerals which are
smelted as ores for iron, — it is found almost pure in masses
of meteoric iron and in a vein traversing mica slate in North
America. In combination as an oxide, it is extensively dif-
fused, being found in small quantities in most minerals, and
consequently in the soil of the earth’s surface. It occurs in
many springs, being dissolved as a protoxide by water charged
with carbonic acid, and then again deposited as a peroxide,
either at the bottom of marshes, as bog iron, or on the hanks
of the springs : and it is deserving of notice that this appa-
rently simple operation is sometimes compound ; the tangled
masses of this substance, so frequently found in such situations,
proving on examination to be the work of an infusorial animal,
— the gaillonelta femiginea, — which thus interposes and reduces
the mineral to an animal substance. This metal is also found
in the colouring matter of the blood, of the hair, and of many
other tissues, animal and vegetable, and its uses are not there-
fore limited to the great works of art, — the machinery of civilised
social life, — but may be traced in the many charms which are
shed over life itself, by the varied colours exhibited, under the
control of creative power, in the petals of the flower, the egg
and feather of the bird, or the skin of man and other animats.

I fayamt enters into the composition of a great nu mbe r of
minerals, though often in a very small quantity, forming, in sneh
cases, their colouring matter. It is abo found in the ashes of

SUDtlf EKTABY GEOLOGY.

w

plant* and the bows of Animals. It i» used In the arts, — for
preparing chlorine by the action of its peroxide on hydro-chloric
acid, and oxygen by the action of the same oxide on sulphuric
acid ; as also to deprive glass of its colour hr the oxydating
action of it* protoxide, or to colour it purple by its deutoxide.

These, then, are the simple elementary substances which have
hern combined together in that portion of our globe which, by
the long-continued action of meteoric agencies, has been reduced
to a condition suited for the support of animal and yegetahla
organisation ; and they will next he considered in the miners}
compounds which form the strata of the earth. These are few
in number, for creative power having combined a few element*
into a great variety of forms, just as we observe in the organic
world in which many substances, Ixvth animal and vegetable,
possessed of the most opposite qualities, — some being alkalis,
some acids, some poisons, some wholesome food, — hate all
been compounded of the four simple elements, carbon, oxygen,
hydrogen, and aaote. One point, however, is here deierving
of especial notice, as bearing on the great question of th*
former condition of our glol* ; namely, that {rd* of the pon-
derable matter of the earth's crust, taking into consideration
oxygen, hydrogen, ami carbonic acid, hare existed, or been
capable of existing, in s gaseous state.

The principal minerals which enter into the composition
of rocks, and of it ratified beds, are — quarts, felspar, mica,
augite, hornblende, oxydulated iron, carbonate of lime, sulphate
of lime, double carbonate of lime and magnesia or dolomite,
chloride of sodium or rork salt, coal, and lignite. Many other
minerals occur occasionally in rocks and sedimentary deposits,
and impress upon them a consequent peculiarity, such as
garnet in mica schist, tourmaline in some varieties of granite.
Hints in chalk and other calcareous formations, iron pyrites
and carbonate of iron in shales, crystallised carbon or the
w*mI amongst the gravel and other transported or alhmal
matter along the Ghauts in India (especially at Goiconda), as
also in Borneo and b Brasil ; but these, as wefl as the vast

n

mrDlUENTART GEOLOGY.

variety of minerals found in the basaltic and trachytic Ians of
both ancient and modem volcanoes, and those either associated
with metallic ores or isolated iu mineral veins, although replete
with interest to the Mineralogist, and often of great value to
the carefully inquiring Geologist, are insignificant as to quan-
tity, when compared with the minerals cited as the principal
constituents of the earth’s crust. The composition of these
minerals may be represented in a tabular form, as in p. 32, and
to them, as principal elementary substances, mar be added the
alkali lithia, its name, derived from the Greek having

been adopted from its first discovery in an earthy mineral, though
it occurs only in small quantity in rocks. The metallic base
lithium was obtained by Davy from the alkali ; its equivalent is
very low, (5*4 1, and its oxide has therefore a high saturating
power. The discoverer of the alkali was Arfwcdson, in 18 18.

Rock salt is a com|>onnd of sodium 40*3 and chlorine 39*3,
or according to the old view, 33*29 of soda and 46 71 of
muriatic acid, but it is usually contaminated by a small quantity
of extraneous substances, — the salt of Cheshire containing —
Muriate of soda . 98*32 Muriate of magnesia 0*02
Muriate of lime 0 01 Sulphate of lime . 0*65

In dissolved matter 1*00

Coal and lignite van* considerably in composition. Blind coal,
culm, or anthracite, contain* for example from 94 to 97 per
cent, of carbon mixed only with mineral matter, as bitumen
has either not been developed in it, or lias been subsequently
removed, though traces of vegetables have been discovered
even in anthracite; it is therefore a non-flaming coal, and
yielding an intense heat, is particularly valuable for the lime-
kiln and similar purposes : the coal of Kilkenny in Ireland and
the culm of Wales belong to this division. Newcastle coal is
a flaming or bituminous coal, consisting, in the best varieties,
of carbon 84*99, hydrogen 3*23, oxygen 1 1*78, bitumen baring
been developed in ita substance by the action of oxygen and
hydrogen on a part of its carbon. Lignite still exhibits the
structure of wood, and may be considered a fossil chartoaL

mUDlNKXTAftY GEOLOGY.

29

In studying the minerals which are combined together in
the rocky crust of the sarth, attention must be paid to certain
Yariations in the chemical constitution of a mineral which do
not affect its external form— or, in other words, to the great
doctrines of substitution by equivalents and of isomorphism.
It is thus that substances jxmessing the same elementary
constitution may replace each other in a mineral, without
disturbing its principal or characteristic qualities ; for example,
alumina is possessed of the same elementary constitution as
peroxide of fcun, namely, it consists of 2 of base to 3 of
oxygen, and can thus replace it ; ami magnesia, jwssessing
a constitution of l of base to 1 of oxygen, can replace the
protoxide of iron. In green and black augitc this variation in
the bases is well exemplified : as they contain,

Green augitc, — magnesia l T ID -f prot. iron 10 02 = 21*51
Black augitc, — magnesia 4*00 4- prot. iron 1 7'3N ss, 22*37;
the actual comfiosUicm varying whilst tiic formula of composi-
tion is preserved.

As it is difficult to convey fully to the mind of the student,
by written description, the physical characters of minerals, he
is recommended to obtain accurately named specimens, though
a few remarks will l>e given, and may be of use when com*
bined with the description of rocks.

Quarts is well known as rock -crystal, which is often
called diamond, as Cornish diamond, Bristol diamond, Quebec
diamond, although it has not the slightest relation to that
mineral ; and also as common quarts. The prevalent colour is
white: when pure it is either transparent or translucent;
when impure it is commonly opaque. Its lustre is vitreous,
inclining in some varieties to resinous. The streak is white.

Felspar. — Prevailing colour white, sometimes grey, and in
many granites and syenites flesh red ; transparent, translucent,
or almost opaque , lustre, vitreous inclining to pearly on the facet
of cleavage. By observing the tendency to a resinous lustre in
quarts, ami to a pearly lustre in felspar, these two minerals may
generally be distinguished from each other without difficulty*

Rudimentary geology.

An inspection of the Table Trill show that under the head
Felspar is ranged a group of minerals connected together by
general resemblance of composition, but named differently as
potash, soda or lime becomes the leading base. Modern
Mineralogists have in this manner * subdivided the great
group into sections ; and this attention to the chemical vari-
ations of the mineral will doubtless be 'hereafter made an
important help in studying the formation of rocks.

Mien . — Pretailing colours, white, grey, yellow, dark brown,
or black ; transparent and translucent, espedUUy in thin
iamiiue ; lustre, pearly ; flexible and elastic when in lamina*,
by wliich character it is distinguished from chlorite and talc.
This remarkable mineral is at once recognized in granite, gneiss,
and mica slate, by the brilliancy of its plates or laminar.

Talc is distinguished from mica as being flexible but not
elastic : in mtn|K>sitiou it differs from the presence of magnesia.
Talc is one of a group of minerals which includes chlorite.

— Colour varying from green or gTey to brown and
black; generally opaque; lustre, sitreous inclining to resin-
ous ; brittle. This mineral is very common in volcanic rocks.

IlorMendt .— Prevalent colour, shades of green, increasing in
intensity up to black ; generally ojaujur , lustre, vitreous inclin-
ing to j»carly in light -colon red varieties. Brittle when isolated,
but when massric frequently tough, and therefore difficultly
frangible. It is an essential ingredient of syenite and greenstone,
and often occurs in granite, gneiss, and other mountain rocks.

The two last-named minerals are reducible to the same
chemical formula, as they are both bisilkates of lime and
magnesia, in wliich a portion of the add or silica is sometimes
replaced by alumina, and a portion of the base by protoxide
of iron, according to the law already noticed ; they are also an
example of dimorphism, the crystalline forms being different.
The difference of geological pos itio n will enable the inquirer to
judge in most cases whether be is examining the one or the
other ; but as it is sometimes very difficult to determine whether
a rock should be darned with greenstone or with b as alt, to

mCDtMKHTAKY QtOlOOt.

31

it it ftlto difficult to distinguish between these two minerals*
In general the species hornblende contains less lime than
augite, and is less fusible ; but as might have been supposed
from the similarity of their elementary constitution, it is pos-
sible, by adopting certain conditions of heating and cooling,
to change the external crystalline form of tbs one into that of
the othrr ; an experimental fact which lias been used in ex-
planation of the difference of their ordinary position.

Ihallagr, or Schiller Spar . — (olour, dark olive-green, in-
clining to pinchbeck brown ; lustrr, metallic ; part of a group
including bnmxite and hypersthrnc, minerals which enter
occasionally into the composition of rocks having the general
character of honiblcudic rocks.

Oxydulatcd Iron or Magnetic Iron , a compound, according
to Bcrxebu*, of 2 atoms of jieroxido ami I atom of protoxide
of iron. — It is highly magnetic, and when massive, more so than
any other ore of iron. Colour, iron-black ; opaque ; lustre,
metallic. It forms extensile bed* in Norway mid Sweden : at
Dannemora the beds are excavated to the day, the principal mins
forming a chasm of 150 ft. broad, and 500 ft. deep. The amor-
phous m&s»c* of St l>e ns and thr Ilartz, which yield the most
powerful natural magnets, may be associated with this *f*eciej».

Carbonate of Lime, and alto Double ('arltanate of Lime and
Mag* et\a, or Dolomite. — The presence of carbonic acid can
always be determined by the action of an acid and the con*
sequent ebullition produced by the eacayie of the carbonic acid.
Thii i* the easiest and most certain method of detecting lime-
stooe. Sulphate of L*me is distinguished from carbonate by
not effervescing with acids , and from other mineral*, whether
in it* fibrous or lamellar state, by tu oomfianitive *oftnr»».

Of salt, coal, and lignite, it is unnecessary to say more
under this head.

Bach then are the mineral* which enter extensively into the
composition of the earth'* crust ; and in order to form a dear
kk* of it* present and past condition it is necessary to inquire
under what combination* they usually occur*

32

rudimentary geology.

mtHXHTAIY GEOLOGY. 33

A surrey of any extensive portion of the earth’s surfkoe
will generally bring before tts two distinct forms of mineral
compounds ; one, in which the constituents occur in dis-
tinct crystals, which to the eye exhibit no traces of any
prerioos wear, and produce therefore by their combination
crystalline rocks ; the other, in which the constituents have
undergone wear, are either mixed together confusedly or
separated into distinct beds, and, whether loosely aggregated
or cemented together, indicate the action of various meteoric
and mechanical agencies and produce rocks of dejmsition,
whether mechanical or chemical. To the first class belong —
granites, syenites, greenstones, basalts, gneiss, many varieties
of mica slate, granular limestone ; to the secoud — sandstones,
conglomerates, shales, clays, comjiart limestones ; uul if these
forms were always distinctly marked, the divisions would be
sufficient and satisfactory : but when the cry stalline rooks,
formerly called primary, are closely examined, some of them
are found to resemble the sedimentary, as for example, mica
slate and clay slate, some varieties of which are little more
than a highly indurated shale ; and in like manner sedimen-
tary rock* in the vicinity of anrirut lavas are found to have
undergone a change in their characters which assimilates them
to the crystalline rocks, whenre even the strata are full of
organic remains ; and on observations of this description the
metamorphtc theory has been established.

If the Geologist, liaving by a careful scrutiny determined
the composition and physical characters of the various rocks
he meet* with, were to proceed to explain their occurrence
an hypothetic assumptions, he would fall into the specu-
lative errors of his predecessors ; hut he pursues a different
course, and wisely determines to ascertain, by observation,
what forces are still in action on the earth’s surface, and
what effects they produce on its miner*] constituents, lit
thus studies in lavas issuing from volcanic craters tha
effect of igneous fttskm, and in sand and mud banks, still
forming, the effect of aqueous agency; be discovers in
*5

34

RTOIM ROTARY OTOLOGY.

the dislocating action of the earthquake, in the wearing
action of the sea wire, in the accumulating labours of polypes,
as exhibited m coral banks, so many auxiliary or modifying
forces ; he observes on the sea-shore the exuviae or remains of
shell-fish and other animals becoming infested in the deposits
of sand or mud forming over them ; and when he turns to the
rocky strata of the earth now become dry land, he finds
similar evidence of igneous set ion snd of sedimentary deposi-
tion, and discovers animal remains imbedded in their substance.

The metamorpbk* theory facilitates the application of recent
analogies in explaining the condition fit crystalline rocks which
may hare proceeded from a species of fluidity, the result of
direct igneous action, ss in lavas, and probably in some
granites and porphyries ; or have been produced by the
indirect anion of heat on sedimentary deposits, continued for
a long jx'riod arid combined with pressure, as has been the case
in the crystalline schists, snd in some other strata in which
a cry *t alii nr or semi -crystalline re- arrangement of the mineral
particle* has taken place, although the existence of organic
bodies still demonstrate* their former sedimentary character.
By the carrful examination of recent and still recurring natu-
ral phenomena these truths hue been made manifest; and
it is by the continuance of such examination that remain-
ing difficulties will he removed. The change produced on
mineral beds by contact with highly heated matter has been
demonstrated, almost with mathematical precision; and though
it is very difficult to decide its exact limitation, we can never
satisfactorily study the strata of the earth without referring
to it. And if the metamorphic theory thus aids us in study-
ing the varying mineral conditions of the earth's crust, the
organic remains still visibly imbedded in many of its beds
demonstrate that changes equally striking have taken p bee a
the succeastve organic inhabitants of its suriaee ; in short, that
there have been animal and vegetable a well a mistral
epochs. The beautiful combination of facts on which Pis*
Ueentology now rests, a one of the most sort ba s es of geo-

1UDIMXKT41T OlOlOOt. 3$

logical science, can only be ftilly appreciated by oarefal study ;
but in this brief memoir it is assumed as a fact, that at rari~
cue epochs the mineral strata of the surface of our globe were
di stur bed deeply and widely, shales and slates, sandstones and
conglomerate*, limestones, Ac., were formed, some in one
place, some in another, whilst great modifications took place
•imultaneously in organic beings ; and if this statement, which
b founded on facts observed over s Urge portion of the earth,
be correct, the evidence of the e[>ochs of mineral change
should harmonise with that of the epochs of organic change,
and hence the study of the one may be made to assist that of
the other.

This deduction has in a few years elevated Geology to the
rank of a science ; and it may be hoped that a more exart
Study of the operations of the great physical forces which
still set ami always have acted on the earth's strata, such as
magnetism, diamagnetism, electro-magnetism, Ac., as well as
of the effects of s continued contraction of the earth's nucleus,
will render it so practically exact, that not only the probability
(under any conditions of strata) of discovering certain useful
products mav lie stated, but the more abstract and obscure
questions of mineral veins and of the distribution of metals be
solved on sound principles.

It may then finally be assumed, that as mineral matter is now
brought tn volcanoes into that state of semi- fluidity which allows
of the crystallization of minerals, so si former epochs it ex-
perienced a similar fusion, and hener that truly igneous rocks
existed at such epochs, and were brought nearer to the sur-
face, or eveu erupted ; — that, in a similar manner, the changes
produced by slow igneous action under great pressure, having
been observed in strata contiguous to modem and ancient
lavas, they may have occurred in stratg contiguous to other
igneous rocks, and hare given rise either to schistose crystal-
line rocks in all their varieties, or to some simpler modi-
fication of the structure of sedimentary deposits ; — and
finally, that changes in the combinations of organic beings,

36

KDIMXITTAKT GEOLOGY.

having been proved by extensive observations to have occurre d
at successive epochs ; when any particular group of animals or
plants has been studied in connection with the mineral strata
of any one portion of the globe, it becomes a clue to deter*
mine their relation with the strata of any other portion in
which organic constituents have also been discovered. The
certainty thus attained constitutes the value of Geology as a
practical science ; and though much caution is yet required to
remove mere varieties from the lists of characteristic fossils,
and to determine the actual limits of species, it must be ad-
mitted that the modem applications of the science have been
both useful and satisfactory.

A general representation of the combined theories of igneous
rocks, mrtatnorphic rocks, and fos&ilifcrous deposits, is given
in the ideal diagram, fig. 1, extracted from Cotta. In the
diagram, granite is represented as an igneous rock near to the
surface, anil having its origin at no great depth ; and that this
is probably the true state of the case will be subsequently
shown, the low specific gravity of ordinary granites, which
varies from 2\ T> to *2T, whilst that of the lavas of ^Etua,
Strotnboli. and Vesuvius, is 2 * 9 , and that of basalt sbove 3 ,
being a strong argument sgaiust their formation at great
depths, or under great pressure. The chemical investigation
of the composition of rocks as compared to that of their
separate mineral constituents, which is now much attended to,
is beginning to throw new light on their relations to each
other. Plutonic rocks arc eminently siltcioua or quartsose,
and volcanic rocks fclspathic, and it has been shown that the
low specific gravity of the former is closely connected with this
excess of silica. It is therefore by no meaus improbable that
granites may have been formed from the liquefaction of crys-
talline stratified rocks, which they to closely resemble in com*
position, if not of sedimentary deposita.

38

MV D1MSMT JJLY 99QVOGT,

CHAPTER III.

Okolooical Fosmatio** — Tb«r Meaning, Object, and UtilitT — The
Mode of Studying them, and the Phjucal Phenomena they exhibit.

Aw inquiry into the actual condition of the earth’ • crust
has made known to the Geologist, as stated in the preceding
chapter, that the mineral matter of which it consists must,
from the great randy of its characters, hare been produced
under circumstances equally varied. He has thus been led to
trace in variously alternating beds or strata, however indu-
rated, a dose resemblance to the muds, sands, and gravels
now accumulating at the bottom or on the shores of the exist-
ing seas and lakes, and to compare the ancient limestones
with the calcareous debits and the coral banka of tropical
•cas ; he has discovered the affinity between lavas now erupted
by still active volcanoes and the atreams poured out either
aub-acrally or sub-aqucously by the volcanoes of other times,
and has ascertained that crystalline massive rocks, granites,
syenites, and porphyries, were brought to the surface at various
distinct epochs, and were therefore connected with distinct
histone periods of the earth's changes ; and finally, be has
observed and exemplified the alterations effected in the struc-
ture of mere sedimentary deposits by the combined action of
heat and pressure, which have produced that crystalline
structure so common in the metaxnorphic rocks. The know-
ledge thus acquired and the proofs obtained of a certain
sequence and progression in mineral deposits, would not alone
have enabled the Geologist to determine that the alternating
disturbances and changes they shadowed forth were events
antecedent to Man's occupancy of the earth ; but he has

MV DIM KITTLE Y GEOLOGY.

39

found in his researches other evidence, and whilst apparently
engaged only in the examination of the mineral structure of
the earth, has fallen upon the traces of its former inhabitants,
in the many shells and other organic relics imbedded in ita
strata ; and though yielding to a natural impulse, he first called
them by names, such as cockles, &c., which assimilated them
to existing shells, — just as “ the emigrant to a foreign dime
bestows on its fruits and flowers the names familiar to him in
his own,** — and attributed their anomalous position on land to
the Deluge, it was not possible that a careful scrutiny of tho
circumstances under which they occurred could long leave
him without a suspicion of their true bearing on geological
history'. When, for instance, the inquiry was extended from
such fossils as were scattered over the surface or were im-
bedded in loose strata to those which were so intimately mixed
up with mineral matter as to form an essential part of vast
accumulations of solid rocks, as slates, limestones, &c., it
became evident that no single cataclysm or event could account
for their existence in such a position. More careful investiga-
tion, whilst it explained the changes which bad affected their
mineral condition, discovered also differences in organic form
and structure, until st length the prejudice which still sought
to explain such supposed anomalies by the plastic power of
Nature was dispelled, ami the magnificent truth became apparent
and recognised, that Geology teaches the history of past as
well as of present creations. This truth, though previously
imperfectly developed, was first set before the British student
in a clear and distinct form by the late William Bmilb, who,
haring with great labour traced out the continuity of many
of the British strata tnd studied the peculiar fossils which
each well-marked stratum contained, announced as facts—
that

1 . The fossils found in any stratum are the relics of animals
Bring at or about the time when that stratum waa deposited
or formed.

2. The strata not being parts of one confuted mass, but foi»

40

ET7DIXBXTAKY GKO LOGY.

lowing etch other in « distinct progression, and the differences
of their mineral character indicating marked differences in the
conditions of deposit, it must be assumed that the animals
which supplied the organic relics they contain lived at snccea-
«ve, and often widely separated epochs.

3. As the organic differences observable in these relict of
animals of other times exceed in amount and kind any pro-
bable, nay possible, variation of specific characters proceeding
from the influence of local circumstances, it must be admitted
that at each stage rtf the earth’s history there was a distinct
and peculiar assemblage of organic beings which, from causes
not clearly known to us in a final sense, became extinct and
were replaced by others.

Geology therefore rxplnins to us the history of the organic
as well as the mineral changes of the earth, and luring esta-
blished a connection between the two at various q»ochs, em-
bodies the knowledge tlm* acquired in a distinct shape, as
expressed by the term ' Formation,* which implies ‘A History
of the organic and inorganic conditions of the earth s surface
at any given epoch,’ not limited hv time, but by circumstances ;
no that the term ' Silurian Formation* implies a history of the
elianges which took place in the earth's surface, of the volca-
nic eruptions, the various deposits formed by rivers, lakes, and
seas, the modifications effected by the action of currents or the
heating of the waves of the sea, and of the animals which con-
temporaneously existed, at an cjK»ch which, though we cannot
state its antiquity by years of time, was evidently, by the posi-
tion of the strata, posterior to some and anterior to other
formations.

The practical utility of geological formations when thus
established, is this, that having once ascertained that the con-
ditions of the earth were favourable at particular epochs to
the production of certain mineral changes and the existence of
peculiar organic structures, and that creative power had called
into existence the animals and plants which were suited to
such conditions, and left them imbued with powers of en-

KUDIMENTAEY GEOLOGY.

41

during only a limited amount of change, it becomes practi-
cable to proceed in an inverse order and to determine the
geological age of any stratum from the relics of animals and
plants it contains ; and even to use the knowledge of the con-
dition of the earth's surface at a particular epoch, which is
derived from a study of the organic remains of the strata
formed within it, to estimate the probability of finding other
substances whether mineral or organic, metals or coal, to the
existence of which that condition appears equally favourable.

PHENOMENA OF ROCKS.

Before proceeding to the study of formations, the relative
order of which can be determined by comparing together the
natural history of each, that is, the fossils contained or buried
in successive strata, it is desirable to notice those phenomena,
or arridcuts of strata, which have materially aided in first
establishing the fact of succession, and must still be consulted
in all doubtful cases of position.

STHATirif ATION.

Many rocks exhibit a larttcllar arrangement throughout
their mass, which produces a schistose or slaty structure
sometimes related to the greater plane* of supposed defla-
tion, sometimes to a plane intersecting that of drjtositwm,
and called the plane of cleavage. In the first case the
structure may be the result of original definition ; jn the
sect m<l, of subsequent or rnetamorphic modifications. In all
cases where rock* are observed to consist of distinct layers, lying
one over the other, ami each having a considerable extension,
they are said to be stratified. If this stratification had been
found every where uniform, it might have been assumed that
deposition had gone cm rrgularty and without disturbance j
but stratification is often very irregular, both in the thickness
of the beds and m their position and direction, and therefor#
it must be inferred that some interfering cause has disturbed

42

BtOmiVTAlT GKOLOGY

and modified their deposition. Again, if to a succession o t
beds haring a considerable inclination, called * dip/ to the
horizon, succeed other beds, perfectly or uearly horizontal, it
is reasonably concluded that the first beds must hare been
tilted-up before the deposition of tbe undisturbed horizontal
beds, and thus an epoch of disturbance or separation is
established ; the terms conformable and unconformable being
applied to the strata as they preserre or lose their parallelism.

e

Pip. 2 .

-7777777 1

'////A 1

' . ; 1

1 1 :

Mill

iiiM

Thus b is unconformable to a, and c is unconformable to b %
whilst tbe beds of a, b, ami c, arc conformable within them-

•elrrs.

As the true position of erery bed or stratum in the system
to which it belongs must be first determined from the actual
order of auperjioeiticm, although fossils may be subsequently
used to clear up occasional obscurities, the great importance
of accurately studying stratification is evident ; and the occa-
sional difficulties which are met with in the imreatigation may
he estimated from the following examples, in which the most
ordinary cases of doubtful superposition are exhibited. It is
very possible also that the difficulties may be co mpli ca ted by
contortions extending only through the lower portion of a mats,
and producing an apparent but not a real unconibraabtlity.

tTJDIXINTAKT OTOLOGY.

43

Fig. 3.

In fig. 3 the portion x may he found either to overlie or to
underlie the stratified beds when sufficiently ojjemni to show
the connection.

Fig. 4 .

/

/////

/////

>

In fig. 1, though x overlies the stratified beds, it may be
found either conformable or unronfortnablc to them.

Tig. y

In fig. 5, i may other undedift or overlie the stratified beds.

44

KTTDTMBTCTAKT GEOLOGY*

* has in these esses been represented ss itself unstrati&ed ;
it may, however, be also stratified, sod then the following ex-
ample will show the possible results.

Tt g. 6 .

In all of which jr is uncoil fortitalde to *, excepting in the fourth,
where it is conformable to r, although possibly of a different
mineral character.

It will lie observed from these example* how much caution
is m pared in determining the exact conditions of stratification,
and in not too hastily deciding that a rock is older or younger
thau another from its apparent position ; and this is shown
even more distinctly in

RUDIMENTARY GEOLOGY.

45

where a, though generally lower in natural position, as it ia
older in geological age than 6, rises up from below it to a
higher level ; and again 6, though underlaid by a at one
point, rests itself directly ou the subjacent rock at another,
and might be even, from a mere comjuunson of levels, sup-
posed to underlie the elevated jiortion of a.

Strata are frequently undulating on the large scale, though,
when examined at Any one (Knot, they appear to hare a uniform
inclination.

Fig. 8.

This arrangement may l>e due either to original deposition
on a previously modified surface, or to gentle movements of
the underlying mass prior to the consolidation of the overlying
strata. The crest or ridge transverse to the highest [mint Of
each bend, as here shown in section, forms the antichnal line
nearly in the directum of the strike, and a line running in
a similar direction along the hollow U the synchnal line.

AND CONTORTIONS Of ffTRATA.

The undulations above noted art* simple, but flexures and
contortions of strata of the most striking kind are often cxlii-
bited on a grand scale, as m fig. 9 : to illustrate them Sir
James Usll made the following experiment. Several layers
of day were placed under s weight, snd their opposite ends
having been pressed by considerable force more closely to-
gether, it was found on the removal of tbe weight that the
layers were curved and folded so as to resemble, in minia-
ture, the natural strata. Other illustrations have been pro-
posed, hut it may be remarked that in all of them tba
materials acted upon are supposed to lie flexible j whereas in
the crystalline schists, the contorted strata art now so hard

46

ICOmiKTIIT GEOLOGY.

End brittle that they could not be supposed capable of as-
suming such forms without being shattered, or at least exten-
sively cracked at the bends. That internal movements have

taken place, even in the most indurated strata, may be ad-
mitted ; and that one stratum has sometimes been forced over
another, the surfaces being broken up and formed into a
breccia, seems evident from the breenated structure of some
strata ; but in many cases we can scarcely doubt that the now
highly indurated and crystalline strata were, at the period of
flexure, soft and pliable.

In the Carpathian chain, mrtamorphk* rocks including
gneiss, mica schist, talc schist, Hay slate, associated with
syenite and porphyry, are succeeded by an extensive formation
of sandstone. Intercalated with this rock, at vinous places,
are beds of limestone, which, from their fossils (ammonites,
flc.), have been considered either a member of the g re en - san d,
which would place ths whole in the cretaceous system, or
a connecting link between the oolite and the chalk. In either
«*ae the formation is comparatively recent, and at it mm prises
clays and limestone* with the sandstone, it very fevoovable
Jbr studying both the me chanical cflfocta of presence and those

IDOmiKTUT OKOLOOY.

47

of metamorphism. For example, aome of tiie schistose clays
hare become silicious slates, with occasional reins of cinnabar,
the marls hare been converted into jasperoid rocks, and the
sandstones either into quarts rock or into highly quart sose
grit full of pyrites, whilst the mechanical changes during this
metamorphic action hare been as striking as those exhibited
in the Alps in similar strata and shown in fig. 9, already
referred to. In the tertian’ beds of Sicily, where thin bed* of
iobd gypsum are intent ratified with bent and undulating
gypseous marls, the solid beds hare been broken into detached
fragments which still preserve their sharp edges, while the
continuity of the more pliable and ductile marls has not been
interrupted ; an example equally illustrative.

In endeavouring to explain these phenomena at reasonable
objects of srientifir research, too great • stress must not lie
laid on any one emu sc of change to the exclusion of others.
There can, for instance, be little doubt that many minor
contortions, anil some flexures in strnfit, are the result of
their original deposition on banks and amidst the eddies of
currrnts ; but we rannnt ascribe the flexurrs in the Alps,
where, as Lye II observes, " curves of calcareous shale are seen
from 1000 to 1500 feet in height (fig. 9), in which the bed*
sometimes plunge down vertically for a dqith of 1000 feet
and more, before they bend round again," to such a cause,
and must consider them striking evidences of disturbance from
internal movements ; a subject to which reference will be again
made.

The preceding observations are sufficient to show the car*
with which it is necessary to trace the order of superposition
of strata, and to guard against the ambiguity produced by
undulations and disturbances ox stratification, and sometimes
increased by 4 Cleavage/ which will be now considered.

CLESVAGB (jO!WT*LfKS AMD BLATy).

Id strsttficstkm the beds ere the result of saeemtve d*>

earth ft* * planetary IxxJv. in a future chapter they
will W discussed in n*npect to deration, it is only here neces-
sary to observe that the forces which have produced the more
marked ridge* of at ratified deposits appear to Iiavc acted
in lines related to the srrrat circles of the earth. In ciulea*
Touring to discover the limits of successive beds of sedimentary
dejiosits, other planes than those of deposition are met with,
and it ii often difficult to decide which is the true plant* of
stratification, and which the plane of cleavage. There lifts
Wen much olmcurity on this subject, hut accumulated evi-
dence now leads to the conclusion, that the direction of
cleavage is due to the same general causes which affect strati-
fication, as Mr. Sharpe has serially shown in his examination
of the effect produced on the form of fossils. Cleavage planet
are often parallel over a large space of country, cutting through
several distinct geological formations, independently of the
coutortiona or undulations which the strata have undergone,
and of the original bedding, the dip of the strata Wing to the
t. r.., and that of the d ravage perhaps to tW s. w., or rice
rerwrf; whilst the strike of both may W nearly the tame.
Again, the dip of the plane of stratification and that of cleavage
may both W to the t. a. or ft. w., and yet the angles of their
dip may W very different. In tome cases cleavage may assume
a fan-like form, the strike still continuing nearly uniform with
that of stratification, so that the disturbing forces appear to
have acted at successive epochs, nearly in the same direction*
In addition, however, to these great disturbing causes, the
consideration of matter under heat and pressure would induce

rudimentary geology.

49

cleavage of a different character, and it is thus that cross
cleavage, being one form of the joint-like cleavage of massive
rocks, has been probably produced, and frequently also the
lamination or slaty cleavage of slate rocks. The observer
will generally be able to clear up this difficulty by discover-
ing the plane of deposit of particular fossils, or of beds
of flints and pebbles; and if these be wanting, of layers
of clay or of sand, differing in character from the principal
mass he is studying. In stratified deposits, the direction of
the planes of stratification, as they crop out in the cliffs on one
side and slope away on the other, impresses n distinct character
on the surface of the country ; whereas cleavage, Ixung abrupt
and frequently at a high angle, rarely does so, although the
actual direction of great ridges, which is often not quite co-
incident with the strike of the bedding, is due to the same
cause as that which prrxJuccd cleavage. On the other hand,
the great lines or ridges of strata are often rut through by cross
cleavage, and a passage given to rivers across them ; deep nar-
row dcils being the frequent result of cross cleavage, whilst wide
and open valleys are more generally the result of stratification
modified by elevation. The smaller description of cleavage or
slaty cleavage which has been alluded to as probably resulting
from a polarizing action during the consolidation and metamor-
phism of strata is very remarkable in slates, which arc fre-
quently fissile in directions not parallel but transverse to the
stratification ; and something similar may be observed in the
diagonal lamination of sandstones and of the more recent de-
tritic (diluvial) deposits, which may lx* ascribed to a modification
in the arrangement of the particles during the process of depo-
sition.

DENUDATION AND WEAK.

The term denudation strictly means the act of laying hare,
though geologically it re pre sents the result of that operation ;
so that a valley is said to be a valley of denudation when It
has originated from the removal of a large mass of sttperiacmtn-

50

ftCDIMKKTAftT GEOLOGY.

rock. In reality tbit if only one form of the genera! problem
of wear, and yet it deaerret especial attention, as being pecu-
liarly calculated to awaken a lofty conception of the rast effects
produced by the most simple natural causes, and to connect
together the operations of the present and of the most distant
epochs. If it be asked what has been the amount of denuda-
tion, the reply should l>e with Lvrll, — that it may be measured
by the whole mass of our stratified deposits, as they hare
all been detached and removed from their primeval positions.
If the question Ik*, "At whit time did it commence, and
how often lias it been rrpeated ?'* — tliat its commencement
must at least have been anterior to the deposition of the crys-
talline schists of the earliest rpoch, and that it has been
reflated during every successive epoch of the earth’s history.
Such considerations as these will enable the observer to form
a just estimate of the magnitude of the phenomena before
him, and will relieve him from that hesitation to admit their
possibility which is the consequence of a cramped perception
of the forces which produced them. In no other science is
this power of philosophic generalization so important as in
Geology, as the observer is constantly required to pass from
the contemplation of very simple facts to that of great results ;
though at first he is jx-rhaps disinclined to admit or even
unable to comprehend the connection between them.

In sliKlyiug the denudation or wear of the crystalline schists,
a solution is obtained of a difficulty which led into error even
Playfair, who, when discussing the probable thickness of the
known portion of the earth** crust, estimated it from that of
•oceeaatve outcropping strata. For example, in a mica schist
district an unbroken series of strata may be traced for probably
50 or 60 miles, dipping at an angle of 30° or 35° ; and if it
were assumed, wHh Playfair, that all these beds were ori-
ginally deposited one upon the other is a honsontal pos it io n,
and su b se qu ently elevated by a disturbing foror, the thickness
dedaobla from inch a ooaatderatian would be eery ooamder-

ftOMMIKTAKY GEOLOGY.

*1

able. No. 10 represent* a section through strata which hart
for 30 miles a dip of 30° ; now if this deposit had been once
hortsonUl, and then simple tilted up, the thickness would bo
30 sin. 30°, or 15 miles, and the edge of each stratum must

Fl«. 10.

hare been raised about 12 miles above tHh horixontal plane.
With a dip of 45 a , uot unusual in the crystalline schists, tlie
thickness would hire been 21 miles, ami the rise of the
stratum edge 15. Though the inclination of strata lias some*
times resulted from original deposition on banks, it must be
•scribed principal!?, in this description of strata, to subsequent
disturbance, as it proved by the frequency of contortions in all
districts of gneiss and mica schist. Whoever, indeed, has
carefully examined such districts must hare noticed the re-
peated alternations of certain sets of strata, such as quarts
slate, thick beds of quarts with micaceous specks, grmnitiform
gneiss, mica schist passing into gneiss, mica schist passing
into clay slate, layers and beds of granular limestone, 4c. ;
which, if all considered independent and successive beds,
would imply first an extraordinary amount of variation in the
force* acting during their production without a ay great dis-
turbance, and then the action of some great and controlling
force, sufficient to modify the whole mass through a thicknesa
of 30 miles, disturbing and elevating it at the same time;
whereas a lateral pressure, whether produced by the undu-
lating movement of the still liquid nucleus of the earth or
by intr u s io n of liquid igneous matter, taplaim the phenomenon
in a more simple way, by representing these alternation! aa

52

RUDIMENTARY GEOLOGY.

foldings of the strata in contortions, many of which are still
visible, whilst others have been truncated by denudation, in
the manner shown in No. 11, the surface haring bpcn further
modified, by subsequent wear and the removal of the softer
strata, so as to f inn mountain and valley.

11

(ontcjrtrd if rat a, removed, cl*ove the line, by denudation.

Undulating beds were frequently formed during the car-
boniferous period, and the descending or dipping portions have
sometimes been so perfectly truncated by denudation as to
.exhibit on the surface of the soil a horizontal plane. In the
shales of this formation, numerous striking examples may also
he found of wear, prior to the dq>osition of the overlying beds,
by which the observer is enabled to trace the direction of the
current which produced them.

The section by I>r. Lussrr, taken in the Alps from St.
Got hard to Asti, on the Zugersee, part of which is shown in
fig. 9, is replete with fine examples of contortions. The strata,
although greatly changed by mctamorphic action, are not
older than the secondary period, as they contain cretaceous
fossils : they are, however, in immediate connection with
crystalline schists, especially gneiss ; and it seems probable
that some partial modification of structure, whether from
heat or other cause, most have preceded disturbance, and
hart t en dere d them suftdently te na cious to undergo contor-
tion, which extendi to bends of 2000 feet m extent. The

* KomMimit giology. ^

boDovi cot in their tuts mils mark also the greet denudation
which has been effected at points now so derated.

The contemplation of such facts prepares an observer to
expect the vast amount of denudation he will find displayed
before him. It has gone on at all periods, and wherever one
formation is laid hare by the rr moral of the ovcrljing strata,
evidences of its previous wear may be discovered.

ran.Ts.

The preceding phenomena hare implied lateral movements
and pressure, accompanied or followed by extensive denudation
or wear. The present are the result of vertical movements,
by which whole masses of dislocated strata have either slid
down or been forced up, the same strata appearing thus, as if
repeated, at a higher or lower level. In this case, then, the
retaining force in lateral, and the moving force either directly
vertical, or indirect I v so, as the result of lateral pressure ; ami
it is probable, from the frequency of fnults in shale districts,
(hat thr sliding was similar to t hat, of land slips. In fig. 12,
the bed a has been first up-thrown along the line or fault d f
to n 1 , and subsequently down-thrown along the fault fh to a*,
the corresponding portion of a being depressed below A.

F*. 12.

Although great and striking, the actual amount of vertical
disturbance, as exhibited in faults, is generally small as corn-

M

RUDIMENTARY GEOLOGY.

pared with that of lateral aa displayed m contortions. In’ the
Newcastle coal district, the upward or downward movement
has amounted to nearly 1000 feet, so that the surface must
hare been originally affected to that extent, portions haying
been either raised or sunk 1000 feet ahoTe or below the rent.
The projections or inequalities produced by such morement
hare been subsequently removed by denudation, and their
former existence can only l* discovered by studying the
internal structure of the disturbed strati. In addition to
the forces which hire tended to rlerate or depress the crust
of the earth, and either to disturb and contort the strata by
forcing molten mineral matter amongst them, — or, in the ease
of faults, first to fracture and then to separate one portion of
them vertically from the other, — another may he traced in the
effects of unequal contraction on such raried substances, as it is
highly probable that heat gradually accumulating at certain
points dried the superincumbent strata of deposition, and
caused them suddenly to contract and crack. On every aide,
then, and at every level, whether we look at the varied surface
of our earth as it now exists, and as it is now exposed to the
incessant wear of rains, of torrents, of rivers, and of seas, —
or seek our information of its condition within the deep re-
cesses of the excavated mine, — we find the same tale narrated,
of continued disturbance and wear on the one hand, and of
renewed formation on the other.

further Errsc-rs or formative and destroying

CAUSES AS EXmitTED IN MODERN AND ANCIENT SEA

CLIFTS, SEA REACHES, GLACIERS, AND ICERERGS.

8© long as the worn materials of the earth’s original emit
are studied only in deposits which afford no evidence of the
existence of air-breathing animals and plants, it is not to be
expected that the action of wives on the sea cliffs, which
depends on a partial exposure of their surface above the level
o f the sea, should be di s co ve re d . The vast beds of sand-
stone and c p pgi o Bt nte which occur at certain g eological

KVDtMtNTAlT 0*0 LOOT.

55

epochs are records both of we* r sod deposition, of which
the simplest analogue will be found in the accumulations of
sand ami gravel which now form submarine banks. The ex-
tent of known sea banks, such as the banks of Newfoundland
and the Bahama bank, is sufficient to sup|>ort and confirm
such an analogy ; and when it is considered tliat soundings
of only moderate depth are obtained on these banks in the
midst of the ocean, they may be fairly considered as analogous
to and commensurate with any of the more ancient hanks
which now oonstitnte our beds of conglomerate or of sand-
stone. Ancient sandstones and conglomerates were indeed
formed by the gradual accumulation and alternation of sand
and gravel, just as our modern banks are formed and extended
by the action of marine currents, combined with that of floating
fields atul bergs of ice, which have conveyed to and deposited
on them the detritus of distant regions. In the hydrographic
instructions issued by the Admiralty, it is enjoined that the
deep sea had shall l»e cast at convenient periods, even where
no shoal is either known or sus)>ertrd to exist ; and much
valuable data will be thus acquired for determining tlie pro-
gress and changes of such deposits. Every time the lead
touches the bottom, a point of comparison is obtained, and a
datum for future investigation secured ; and when a shoal is
first discovered, blame should not be imputed to preceding
voyagers, as it is probable that in their time it had not been
raised within the reach of ordinary sounding*.

If it were in our power to examine the internal constitution
of sea banks, the occurrence here and there of the trunk of a
water-logged tree, or even of the hard fruits of many plants,
would be ascribed to drift ; but if beds of lignite or fossil
wood were discovered, we should infer from them that the
bank bad either been exposed to the air, and supported a
growth of air-breathing plants, or had been formed in some
ancient estuary, adjacent to rivers whose banks had been
clothed with plants. In a similar manner, though the occur-
rence of fragment* of rocks renders k

$6

RODIMEKTARY GEOLOGY.

probable that other parti of the earth at the time of their
formation supported a growth of plants, it does not prove
that those individual rocks had been clothed with vegetation ;
whilst the existence of beds either of lignite or of coal in a
formation does prove that its strata had either been covered
with plants or were contiguous to other parts of the earth
then covered with them. Such is the evidence afforded by
the ancient beds of anthracitic and bituminous coal of the
carboniferous and oilier strata, aud of the lignites of the still
more recent ternaries ; and as the occurrence of deep beds of
coal marks the existence of forests of tropical plants prior to
their deposition, it is proved that at a very remote geologies^
epoch some portion of the earth s surface had already emerged
from beneath the water, — a fact which is supjiorted by the
appearance even iu the crystalline schists of that description
of wear which is produced by the surge's of the ocean, when
beating on the shore they either shajie out sea cliffs, or form
gravelly and sandy lieaches.

The old red sandstone which underlies the coal strata pene-
trates into the recesses of the mica schist in district* where the
two are in contact, whilst the wear of the crystalline rocks, and
the fragments broken from them and found in the old red
sandstone conglomerates, show that the former had sometimes
attained their crystalline condition prktr to the drfiosition of
the latter. The broken and nigged edges of the mica schist
corresjKHid to the wear of such a rock ; aud the beds of shale
of the coal series exhibit wear still more strongly ; for though
it is often difficult to trace the chfft or sea boundaries of these
ancient period*. as most of the strata have again been sub-
merged aud eoverrd br more recent strata, the presence of
large pebbles of mica schist in the conglomerate formed in
the ancient bay* or recesses of that rock proves that the sea
once beat against it, and the deep precipitous banks which are
not uncommon in the carboniferous formation may be also
ascribed to a similar action. In the ease of Lough Erne, in
Ireland, an ancient sea bottom is observable in the limestone

WLV dim ehta&y gkology.

57

of its shore, which is core red with projecting corals, now ex*
posed by the removal, from denudation, of the shale above it,
just as the sea bottom in warm climates is covered over by
corallines. Shore wear may be traced at every geological
epoch ; but after the deposition and consolidation of the chalk
it becomes more apparent, as the strata subsequently deposited
were less extensive and more local. Sir C. Lyell gives several
examples of inland chalk cliffs which occur in Xorinamlv, but
none can be more striking than the curved escarpment of
cli&lk which bounds the plain of Dungivcn, in Derrv, the
tertiary clays with their marine shells occurring at its base,
and marking in the most striking manner the boundary of a
former sea Uutoin, at levels now raised by elevation '200 feet
above the present sea, although the ancient sea cliff was, as
the present one is, n chalk cliff. As we advance further, new
evidences of continued change are met with m the occurrence
of more modem sea beaches, winch are now far removed from
the action of the existing aca ; and in the cave of I'ddrvalla,
in Sweden, this change of level was long since established by
the ctrrhipeda found adhering to its walls, and identical with
those which now attach themselves to the rocks of the sen
shore. We are thus, by the combined evidence of mceltnnieal
wear and of organic fossils, carried bock step by step to agrs
which, though beyond the reach of histone records, can thus
be compared with the present ; and when the organic links of
identity can no longer lx* discovered, we can still trace in
mechanical effects the working of similar causes up to the
remotest epoch.

The enormous wear effected during the last pause of elevation
prepares us to estimate that of former epochs ; for example,
the wear displayed by tlur present condition of Portland Island,
now cut off from the mam land by the removal of an underlying
blue day, and the consequent undermining of its more solid
strata. At present, the Cbeail Bank, an accumulation of sand
and gravel, forms a natural breakwater, and lessens, though h
does not stop, the p r o gr ess of wear ; but should another slight
c5

58

EUDm Iff TARY GEOLOGY.

deration bring up the bine clay nearer to the water’s edge, the
wear will again advance with rapidity, and the island once re-
moved, the Chesil Bank itself will speedily be destroyed, and
the sea advance upon the main Jand. This case is of ranch prac-
tical value ; the wear of Portland Island is delayed by the dip o t
the beds, which carries the subjacent day to a depth beyond
the action of the moving wave, and reduces the wear to that of
the more solid rock : the Chesil Bank has been formed because
the still projecting portion of solid rock checks the force of the
current, and causes the deposition of the pebbles moving with
it : the jiebbles of the bank protect the subjacent clay from
/urther wear, and thus the general tendency is to preserve a
tottering equilibrium, which the slightest change will destroy.
In this instance a renewal of elevation would lead to renewed
destruction ; in others, elevation may bring up a solid stratum
and thereby retard destruction, and these varying results must
have attended elevation at all geological epochs ; and again, if
elevation stop* for a period extensive wear by bringing up and
oppoaing to the efforts of the sea a firmer rock, depression
produce* the same effect by removing s soft stratum from its
action, a* it did at Portland, where the removal of the blue
day beyond the action of the waves was probably the result
of a depression. In examining any coast, therefore, with a
view to judge of its prol»*hle permanency, the following par-
ticulars should be especially noticed : ! »t, the nature of the
shingle or gravel, as showing the direction of prevailing cur-
rents ; Sadly, the prevailing and most powerful winds ; 3rd)y,
position and character of any sheltering barrier in respect to
the prevailing winds ; 4thly, position and character of any
harrier opposed to the prevailing current.

The ancient or raised beaches of former and not very remote
epochs are also examples of the effects of these modifying
causes, and witbemt doubt many such beaches have been
swept away ; an alteration of level, by elevation or diprtnsion,
having Hummed the work of denudation. The proof— a of
wear on the one hand and depos i tio n on the other am indeed

AUDYMSKTART GEOLOGY. 59

only reft in an equilibrium when the forces producing them
irein a state of balance ; and any alteration in the one must
lead to a change in the others.

Vestiges of ancient river as well as lake wear may also
be discovered; of the former, an example is given in fig. 13
and fig. 14, at the end of the chaptir, in which the former bed
of the river Burnthollct, county of Derry, apj>cara to have
been 10 feet higher than its present course, as shown by the
remarkable masses of rock still remaining to attest the ancient
wear of its waters ; of the latter, the parallel roads of Glenroy,
so often quoted, may be again cited here. These roads are
ancient shelves or beaches, formed at the margin of a former
lake, and at levels cormq>onding to its successive depressions.
The highest is 1250 feet above the sea, the next about 1000,
and the third 50 feet lower. 8ir V. Lyell remarks, that ‘'among
other proofs that the parallel roads have really been formed
along the margin of a sheet of water, it may be mentioned, that
wherever an isolated hill rises in the middle of the glen above
the level of any particular shelf, a corresponding shelf is seen
at the same level, passing round the hill, as would have hap-
pened if it had once formed an island in a lake.*’ The great
lakes of America exhibit similar lake beaches at various ele-
vations above their present surface ; the absence of marine
shells concurring with other circumstances to remove such
accumulations from the list either of ordinary marine beaches
or of sea banks.

But in addition to gravel deposits of this kind, the researches
of Agassiz have added others, — the effects of ancient glaciers.

It has been long known that these vast accumulations of
frozen snow are in motion, proceeding from the higher valleys
of the Alps, where they are formed, to the lower, where they
are gradually melted ; the portion rut off or melted at the lower
end being replaced by a new mass added at the upper end. At
it moves along, the glacier carries with it the fragments of fork
which, having fallen from the p r ec i p i ces above, are arranged
•poo it in Hoes of deposit, to which the name of moraine has

GO RU DIM EHT AJLY GEOLOGY.

been given. M. Agassis distinguishes three varieties, — literal,
in which *the moraine borders the Talley of the glacier, resting
either on it* surface, or between it and the side of the vaUey ;
— - medial, in which the moraine is formed of a long line of debris
stretching, like a riband on the surface of the glacier, down
the course of the Talley ; — terminal, in which the moraine is
seen at the lower or terminal end of the glacier. These forms
of graTel deposit, interesting as regards the history of the
glacier itself, Inromc still more so when applied to the explana-
tion of gravel dcjiosiu, now no longer connected with glaciers.

It will be readily conceived that any considerable variation
in the temperature of the air must prcduce a similar variation
in the amount of snow and ice, and an augmentation or a
diminution, as the case may he, in the glaciers resulting from
them. Within very recent times, the variation has been to-
wards an augmentation of cold, as shown by the inquiries of
M. VcneU on the variations of the temperature of the Swiss
Alps ; but if compared with still more aucicut epochs, the
evidence is in fa\our of a rise of tem^rature. M. Veneta
establishes the first of these positions by historical monuments
and documents, which prove tliat some of the Alpine passes,
now scarcely practicable, were thru the ordinary lines of com-
munication. In the archives of the Commune de Bagnes,
M. Rivas fouml the rrcord of a legal process between that
commune and the commune of Liddcs, relative to the posses-
sion of a forest then on the territory of Hagnes, but which
has sines disappeared and been replaced by a glider, now
entirely cutting off the communication.

Many other examples are cited of the extension of the
gliders within the last 200 years ; bat the amount is small
when compared with their vast extension, as proved by the
existence of indent moraines, in periods beyond the retch
of historical records ; for, as M. Agassis observes, — “ we shall
be forced to admit that many moraines, hr distant from
existing glaciers, must have been formed at the moat remote
periods* if not anterior to the creation of man.** The careful

RUDIMENTARY GEOLOGY.

61

examination of those deposits, which he thinks may be classed
with moraines, has led him to trace, assisted by other phe-
nomena of glacial action, the former existence of glaciers in
countries now far removed, by their comparatively elevated
temperature, from the sphere of their production ; and he has
thus brought the British Islands within the range of ancient
glacial action.

Such inquiries and reasonings lead to the belief that there
was a period of intense cold, when ice ami snow were spread
over a large portion of the northern hemisphere ; and if on the
lands of that froien epoch, the glacier descended, as it now
docs in Spitsbergen, to the sea, icebergs and floating sheet
ice must have been also formed, and the sea covered with*
them. Glaciers were the carriers on land of those fragments
which formed ancient moraines; — icebergs and floes were the
carriers on sea of those vast fragments which now ns * erratics'
are dotted here and there along the course of the then marine
current, just as the modern floe or iceberg now leaves at the
bottom of the ocean, where it ground* and melts, the fragments
of rocks it has carried along with it. This period of intense
cold is called by Geologists the glacial epoch, and it is very
remarkable tliat no traces of glacial action hare as yet been
found in the earlier strata.

It is thus that the Geologist, in endeavouring to trnre out
the sequence of stratified deposits, has been led to discover
and examine the various change* which the earth’s crust
lias undergone at successive epochs. He has seen sea and
land alternately rising and sinking before him ; and standing,
as it were, unmoved on a rock, has watched and recorded the
effects of each movement as it rota and fell. lie is now,
therefore, in a condition to compare together all the results he
has observed, and to frame into one system the mineral and
the organic histories of the earth's changes, as recorded in
the strata of deposition.

GKO LOOT

RUDIMENTARY GEOLOGY,

68

CHAPTER IV.

Plutonic. MeUmorphic. and Volcanic Rock» — Condition and Temperature

of the Interior of the Earth — Dyke* — Elevating Force* — Vein* —

Metallic Deposit* — Economic Value and Usee of the Rocks described.

In passing from one epoch of deposit to another, rocks hare
been observed, which, being crystalline and massive, have evi-
dently undergone igneous fusion, and yet do not resemble
volcanic rocks ; others which, though crystalline, are as regu-
larly stratified as sandstones and shales , and others which are
readily recognized a a volcanic product*.

These rocks ire the subject of this chapter, as it is neces-
sary that the Geological Student should be made more fidly
acquainted with their nature, and with the circumstances con-
nected with their production.

first group.

The remarkable group of Plutonic rock* may be associated
as felspathtc with the well-known rock called granite, of which
felspar is an essential constituent.

Granite, common. — Felspar, quartz, and mica, disseminated
in nearly equal proportions ; the felspar lamellar, and the
texture often granular. Tourmaline and hornblende are fre-
quently accessory ingredients, and many other minerals occur
occasionally, either disseminated in the mass or in veins.
Colour, which depends materially on the colour of the felspar,
b either greyish or reddish.

Gromit, po rp ky r it ie . — Crystals of felspar h> a small -grained
granite. It b o ccas i on a ll y difficult to separate thb rock from
tome varieties of protogrnc.

Granites are divided by joints or planes of cleavage into
irregular polyhedral masses. The metals which occur, either

64

RUDIMENTARY GEOLOGY.

disseminated or in veins, are principally tin, uranium, gold,
silver and its sulphuret, oxydulous iron, bismuth, &c.

Protogyne, green. — Felspar, grey and red, — talc or chlorite
of a deep green : green is the predominant colour.

Protogyne , red. — Felspar, grey or red,-%dc and steatite,
reddish brown or green, the red prevailing.

Such may be considered the characteristic or peculiar mine-
ral components of protogynes ; but M. Delesse has shown that
they generally contain five minerals, — namely, a felspar in
which potash abounds, a felspar in which soda prevails, a mica
of magnesia and potash base, a variety of talc,' quarts.

These rocks arc bedded on a grand scale more decidedly
than granites, and form the highest peaks of the Alps.

Syenite. — Felspar, quarts, hornblende ; the felspar lamellar,
and often predominating. This rock has been subdivided into
sections, such as granitoid, where mica occurs in small quan-
tity ; |>oq>hyritic, where Urge crystals of felspar are imbedded
in a small grained syenite , rirconian, hypersthenic, dialUgic,
according as one or other of the minerals zircon, hypersthene,
diallage, replaces in whole or in part either the hornblende or
the quartz. Some of the varieties, particuUrly the schistoid,
connect the granites with the greenstones, and some are so
similar to metamorphie rocks as to make it doubtful whether
they hare a claim to he considered nicks of fusion.

Pegmatite . — Felspar and quarts ; a silvery mica of potaasic
base is frequently present, as also tourmalioe. The quartz is
often arranged in broken lines, and produces that variety
known as graphic granite, from the resemblance of the quartz
lines to Hebrew characters. The febpar combines the two
bases, potash and soda, — the former being to the latter in the
proportion of 10 to 3 per cent. The quartz sometimes occurs
in grains, and passe* by the introduction of mica into granite
or gneiss. Pegmatite is a variety of the granite group, very
rich in silica, of which the proportion rises so high as 78 per
cent. The finest kaolins, or porcelain days, are produced by
the decomposition of pegmatites.

rudimentary geology.

65

SECOND GROUP

comprises mother extensive family of rocks, of which green-
stone is a type, tta predominant constituent being hornblende.

Hornblende — Base, hornblende with mica, felspar,

garnets, &c. Texture lamellar, and structure sometimes
massive, sometimes fissile.

There are many varieties of this rock, such as the granitoid,
the serpentine, the micaceous, the schisto»d, Ac., so named
from the peculiar mineral or structure which prevails ; and it
is thus that the rock assumes by turns the true character of a
plutonic rock, or those of the metamorphic series.

Greenstone ( Diorite , «$r ) — Hornblende and compact felspar,
nearly equally disseminated. This rock is also subject to
numerous variations, becoming granitoid, schistose, jxirphy-
ritic, Ac. The orbicular granite of (Wsica is n greenstone in
which spheroidal masses of hornblende and felspar occur in a
paste of granular greenstone : a similar rock occurs tit America,
in which the spheroids are wry small.

In the pyrurneride, or orbicular poqihrry of Corsica, radiated
spheroids occur in a paste of compact felspar and quartz. Such
forms arc very interesting, as they are examples of concre-
tionary structure, or of a tendency to definite arrangement
within a mass.

The eurites, or felspar rocks and felspar porphyries, will be
considered with volcanic rocks, though they sometimes ap-
proximate closely to the granitic type.

The ncit daw includes the metamorphic rocks, which in
many respects approach very dosely to the plutonic. They
exhibit a schistose ami stratified character combined frequently
with a highly crystalline structure. For a long time both
granites and crystalline schists were eoftaiderrd primary rocks;
and after the igneous theory of formation bad been admitted
for the massive rocks, it seemed difficult to separate from them
a rock composed of felspar, quarts, and mica, and so highly

66 BUDIMEKT4BY GEOLOGY.

crystalline as gneiss. The alternation of gneiss with mica
slate, granular limestone, and day slate under all the forms
of a definite stratification, rendered it, however, necessary to
adopt some other and distinct theory of u* formation. Had
they ercn been homogeneous, or all similar in constitution to
either granites or greenstones, they might hive been ascribed
to a similar origin, and considered portions of the original
crust of the earth ; but no such theory csn account for the
alternation of layers of limestone with gneiss or mica slate.
The same reasoning therefore applies to these as to other
stratified rocks ; and they must be considered ancient sedi-
mentary deposits, on which some peculiar change ha* been
effected, which entirely masks their original condition ; a
change, which is signified by the expressive term metamor-
phous or metamorphic, and is, to a certain extent, not peculiar
to such rocks, as many sandstones, conglomerates, and lime-
stones have been altered, though not to the same extent, from
the loose muddy paste in which they were originally deposited.
The description naturally commences with the rock nearest in
character to granite.

Gncm*. — F elspar, mica, and cpuurtx, — the felspar lamellar,
and the mica abundant, arranged in lines so as to produce a
lamellar or schistose structure.

There are numerous varieties of this rock, as it is sometimes
a distinct granite in texture, and sometimes merges into the
next species, mica schist. It is occasionally talcosr, approxi-
mating to protogyne, — sometimes is porphyntic, and occa-
sionally loses its (|uartx, — whilst in a rare variety graphite in
•tales replaces the mica ; and it may therefore be imagined how
difficult it must be to draw a line of demarcation between some
granitic and gneisiose rocks.

Mica ScAut (QUmmerschiefer of the Germans). — Mica
predominates, and the structure is fissile. Garnets enter as
an accessory constituent into this rock, ss well as several other
minerals. There are many varieties, ss it becom es g neia aos a
by tbs introduction of felspar, granitic by a more irregular

RUDIMENTARY GEOLOGY. $7

structure, porphyritic with t scaly fracture, or merges into a
day slate : it is sometimes talcose.

Clay Slate . — In this rock the distinction of crystalline ele-
ments is lost, b<£ there are frequently accessory crystals of
quarts, felspar, &c., by which it may be approximated to mica
slate, just as that rock merges into it. It is sometimes so
calcareous as to become almost a limestone slate, and the
alternation of thin bands of limestone with the mctamorphic
rocks, especially with mica slate, is a remarkable and inter-
esting fset, strongly elucidatory of their origin. Clay alate is
also occasionally talcose, or becomes a talc slate.

The porphyritic cliaracter, which is common both to the
igneous and metamorphic rocks, has been illustrated by the
researches of modem Chemists, who have succeeded in re-
taining stouy matter in fusion under such circumstances as
should lead to the format ton of crystals in the mass, on
cooling. Various precious gems have thus hern created it;
the laboratory ; and to these ex |H*ri mental proofs of the
manner in which *hc crystals of porphyries may -luxe been
formed, are to he added the researches of Person on alloys,
which have shown that metals combined together in due
portioiis may first consolidate into a definite alloy, on arriving
at a common solidifying point of temperature, and yet separate
afterward*. The fact that such separation often takes place
before consolidation, — the metals not arriving at a common
point of solidification, — had before been noticed ; and both
facta, when extended to stony minerals, are highly explanatory
of the porphyritic condition of rocks.

Some other less common rocks, such as serpentine, will bo
noticed hereafter in reference to their practical value: and
the reader should observe generally, that, independent of any
theory connected with them, massive and metamorphic rocks
appear under several distinct forms common to them both ;
and as this fact is observable also in volcanic rocks, it k
embodied in the accompanying TeUe, u • reedy means to
make the ofaeerrer frauber with each rocks.

RUDIMENTARY GEOLOGY.

69

Before describing truly volcauic rocks, the connection of
plutonic and metamorphic rocks with the leading physical
phenomena of the universe requires consideration. An hypo-
thesis has been advanced in Astronomy, that the now solid
planetary bodies were once in a stAte of gaseous fusion as
nebulous tqatter, and were gradually condensed into their
present state. The figure of the earth, which is an ohlnte
spheroid, has been appealed to in support of this theory, as a
liquid body subjected to the conjoint action of gravity aud
a rotatory projecting impulse would assume such a form.
The figure of Jupiter is also consistent with the theory, but
that of Mars appears as yet opposed to it. If, then, the earth
has passed through a fluid state, the cause of such fluidity
appears closely connected with heat, as an examination of
the temperature of the earth’s crust at various depths show*
that the temperature below the cooled surface increases on
descending, and that at great depths there is still existing
a vast reservoir of internal heat. From numerous observations
made in mines and by Artesian wells in France, England,
Prussia, Russia, and elsewhere, I*eotihard states that the
temperature increases by l y Reaumur, or 2J° Fahrenheit, in
120 feet. M. Reich considers the temperature in the mines
of Saxony to increase 1° centigrade in 4181 m. of depth, or
Fahrenheit, in 135 feet. In a boring in the Military
School at Paris, the increase was found to be 1° centigrade, or
1|° Fahrenheit, for about 96 feet. In Mr. Fox’* experiment*
in Cornwall, the increase was found to be about 1° in 47' i in
those of Mr. Oldham, in the copper mines of Knockmahon,
county of Waterford, 1° in 82*, being a lower rate of increase
than that of previous inquirers. It may be therefore assumed
as a reasonable approximation, though subject to many sari*
stious from the different conducting powers of different strata,
that the temperature increases 1° Fahrenheit in 60 feet of
depth ; and if the rate of increase were considered constant,
there would, at 60,000 feet, be a temperature of 1000* or that
of low rad heat ; bat as the temperature will increase with the

70

RUDIMEKTARY GEOLOGY.

depth in tn augmenting ratio, Leonhard tagamet that this
temperature would be attained at about 35,000 feet, being a
depth only double the height of Cotopaxi, the moat remark-
able of the Peruvian volcanoes. Descending still lower, the
temperature, at a very moderate depth compared with the
magnitude of the earth, would be found sufficient to retain
mineral matter in a state of fusion ; and it is therefore un-
necessary to place at a great depth the source of the lava
which is still pouring out in so many parts of the earth. The
stmilarity of lava, wherever found, and the close agreement as
to composition and physical characters of the basalt of ancient
epochs and of that still bursting through and intersecting the
walls of modern volcanoes, arc further proofs that all such
eruptions have a common origin, and are due, as well as the
accompanying physical phenomena of earthquakes, to forces
acting on the still liquid portion of the earth.

If then the original igneous fluidity of the earth, and its
gradual cooling from the crust downwards, be admitted, it has
been demonstrated by Fourier —

1. That the cooling of the earth, and the increase of tem-
perature in proportion to the depth below the surface, has
been muck greater formerly titan it now is.

2. That more than 30, IKK) years will be required to lessen,
by one-half, the present rate of increase of temperature ; that
is, to reduce the increase to in 60 feet.

3. That the effect of central heat is now scarcely perceptible
on the surface, not raising the thermometer

4. That for nearly 2000 years this effect has not diminished
by and that in this, as in all the great phenomena of the
universe, a marked character of stability is perceptible.

The density of the earth affords another means of judging
of its internal condition. It has been stated that the density
of the crust lies between 27 and 2 9 ; bat the density of the
whole earth, derived from pendulum experiments, of which
more will be said when treating of ekratory form, t* about
6*5 j so that it ie evident that the ponderable matter of the

BVDIMKNTAftY GEOLOGY.

71

interior of the earth it very much dcuter than the matter of
the entity which it quite continent with the previous suppo-
sition of original fluidity ; for though gates mutually permeate
each other and diffuse themselves, liquids, when they do not
exercise a chemical action on each other, obey the ordinary
laws of gravity, and arrange themselves in the order of their
density. The density of basalt does not usually exceed 3*1,
so that the difference observable by the Geologist in the den-
sities of rocks is very small. The radius of the earth is
3908 miles ; but if we suppose it 4000 miles, and divide it
into 10 equal parts, and then assume that in descending the
density increases in an arithmetical progression by about
1*5 for each part, the problem will he thus stated: the
average density in the first annular space of 400 miles will
he 2*7 ; in the second 4 2, and so on, — the density of the
last 400 miles being about 16 2; a view of the case which
does not appear inconsistent with facts, as it allows an in-
crease in density of 3 for 100 miles, which is probably more
than the thickness of consolidated strata.

The increasing density of the earth, from the surface to the
centre, has an important bearing ou the nature of plutonic
rocks. The density of none of the true granites equals that
of basalt, and it rarely exceeds 2 6, so tliat it is highly im-
probable that granite has proceeded from a deep-seated source.
Granite does not throw out dykes either cutting through tha
strata or Ailing up cracks produced by fracture in them ; its
veins are principally confined to the metaroorpbic rocks, amt
it does not exhibit lava currents . it may therefore be con*
sidered a lower portion of the immediate crust of the earth
which has been liquefied end forced to the surface at various
epochs, but has not been erupted. Tha full development
of crystals in these rocks requires slow cooling but not great
pressure, and there is therefore no reason for supposing that
they were ever far below the surface.

la extending the inq ui ry to the crystalline schists, it will he

72

ftUDWEKTAlT GEOLOGY.

naturally asked whether any portion of them may be coo*
stdered 4 part of the crust of the earth as it was at first cooled
down and consolidated. The alternation of limestone and of
micaceous beds with the more crystalline schists confines this
qncstkm within very narrow limits, and if any rocks now
risible can be supposed not to hare passed through the
sedimentary stage, they are probably only such rocks as the
highly inclined and distinctly bedded varieties of protogvne
which occur in the Alps, — being neither distinctly massive
nor distinctly stratified. There is a similar difficulty in deter-
mining whether the homblendie rocks associated with the
crystalline schists are metamorphic or volcanic rocks. Their
density being nearly npud to that of basalts, assimilates them
to erupted roph* ; and modem Geologists have discovered so
strong a resemblance between some of the strata associated
with the crystalline schists and the ashes, iapilli, Ac. of
volcanoes, as to strengthen the belief that lava currents
have been instrumental in the production of some metamor-
phic strata. Tins portion, therefore, of the Earth's Mineral
History is a fitting introduction to the next, in which the
product* of volcanic eruptions are recognised by their simi-
larity to and even identity with the mineral matter erupted
from volcanoes either now existing or which have existed
since the earth’s surface assumed its present form, though
now extinct.

The truly volcanic rocks have been divided into three arc-
tions, — trachytic, basaltic, and brie, the last of which are now
observed amongst volcanic erupted substances whilst dykes of
basalt penetrate the walls of volcanic cones.

The trachytes are feispathic rocks, coonsting of a highly
crystalline paste of compact felspar, with crystals of sugite
and other minerals disseminated in the mass. Domite, por-
phyrttie write, pumite, pboooiite or clinkstone, belong to the
division ; and there is a trachytic breccia to the prodactiai
of which mechanical action has contributed. Trac hytes
occur in ooantriai where volcanoes art still in action aa wgfi

mUDTMKNTARY GKOLOGY.

73

as in those where they hare become extinct, and they appear
to hare proceeded from a source immediately %elow the
granitic crust. The chain of the Caucasus Hungary, Tran*
sylrania, Auvergne, Isles of Greece, Italy, &c., and the
counties of Antrim and Down in Ireland, are good localities.
Trachyte, as Andesite, acquires an enormous development in
Sooth America, in the chain of the Andes of which it forma
the summits, the beds being sometimes 14,000 or even 18,000
feet thick, as at Chimboraso and the volcano Guagua-Pichincha,
and it is also observed in the Tolcanic districts of New
Zealand. Trachytes are sometimes covered by tertiary
strata, but never by the secondary or older strata, and it
has therefore been assumed that the epoch of their first ap-
pearance is that of the earlier tertiarics. In Auvergne they
often form the boundaries of ancient and partially destroyed
volcanic vents ; and it is not improbable that in like manner
the Antrim and Down trachytes arr jnirtions of the boun-
dary of some great volcanic vent, which occupied the site of
the present Lough Neagh, and through which much of the
basalt of the district may have been poured out.

Basaltic rocks, in which augite predominates in quantity
over felspar, are augitic rather than felspathic rocks, and some
of the varieties which arc highly crystalline like greenstone
out scarcely be distinguished from that rock. Basalt has a
considerable density, ranging to 3'3 in the more highly
augitic varieties; it cuts through granite and every succes-
sive rock, carrying with it and enveloping fragments of the
rocks broken through. The remarkable fines of this igne-
ous matter, which may be sometimes traced for very long
distances, are called dykes, and, when exposed by the
decomposition of the softer strata through which they have
passed, stand out as walls, from which circumstance they have
derived that name. See fig. 15, which is the celebrated dyke
Lady 0*Cax» f s Bridge, and fig. lfi, which represent#

KODtMlirrAKT OBOLOGT. 71

Basalt having cot through granite, must hare corns from
Wow it and the metamorphic schists, though jgfrerr is no
reason for supposing the depth of its source move than
100 Hides. Basalt is rarely found near the summits of
volcanoes, but usually at their base or surrounding them,
and is anterior to the lara currents which overlie it t it la raty
extensively developed in the vicinity of extinct volcanoes, and
is justly considered a truly volcanic rock. In many countrlea,
as in Ireland and Scotland, it is spread out in extensive plains
or beds, which are divided in section or depth into many sue*
sessive laye r s , the structure of which is sometimes globular
and aametlmas columnar, as at 8taffa and the Giant’s Cau s e*
my, and which alternate with beds of ochre or ferruginous
scoria, as well as with beds which have probably been origi-
nally sedimentary, and are therefor* metamorphic. Some-
times, as in the rmakj of Joniilo, in Mexico, the basalt
has been puted up by the elastic gases below into small
cones or bosses, which, having been subsequently cracked,
emit aqueous and sulphurous vapours. These Ilomitos, as
they are called, cover in thousands the great plain of Mai-
Pais, iu which Joruilo rises, so that tbs surface resembles
the bubbles on the top of a boiling viscous fluid. In 1780
the heat of the horoitos was so great that a cigar could he
lighted by plunging it 2 or 3 inches bio one of the lateral
cracks. By the layers of oebreous scoria the mass of
basalt Is divided into successive flows, some of which either
passed over the dried and consolidated achroous mud* or
over the mud still under water where It had been formed
by showers of ashes ; and the connection of irregular or
orbicularly crystallised ba s a lt with cohuanar, the former cap-
ping the latter, is the result of the more rapid flowing and
cooling of the upper portion, A beautiful example of this
effect is exhibited at CnugnahnOiar, in the county of Antrim*
tec flg* 17* b nest page*

76 RUDIMENTARY OSOLOOY.

17 .

The Uric diriitoa can be studied in the phenomena of still
active volcanoes. True lavas have been erupted subsequently
to the basalts ; the lava of extinct volcanoes approaches snore
closely to trachytes, being felspathic, whereas that of existing
volcanoes, being augitie, is nearer to basalts. Successive
flows of lava are frequently sejmated by beds of ashes, scoria,
lapilli, Ac., as may be seen in Use vicinity of Vesuvius. The
eruption, Opposed to be the first of Vesuvius, which in the
year 79 destroyed the cities of Herculaneum, Pompeii, and
Stabiw, and caused the death of the elder Pliny, consisted of
ashes* It is impossible, in this small volume, to describe all
the phenomena of volcanoes ; but the great number actually
recorded is shown by the following approximative Table from
Girardin. And as the number of extinct volcanoes has also
been very great, the eruptive forces of former and of existing
epochs were equal in intensity if estimated fay the quantity of

ftVOIHlIfTlKT QIOLOOY. Jf

'POTfaMMrftfatSMtk.

Oa Ceotiamu.

1* laluadb.

***

Europe . • .

4

20

24

Afrk* . . .

2

9

11

Asia ....

17

29

46

America . . .

86

28

114

Oceania . . .

"

108

108

j ToOI. . . .

109

194

505

Peculiarities of some of the igneous rocks , and the effects tf
igneous , and especially if eruptive rocks, on the earth's
crust ; many of these rocks having been important agents
in the successive disturbances of the earth's surface .

The wide extension of the granite group orer the surface of
the globe must be referred to general and not mere local
forces ; and the frequent co-existence of granite and met**
morphic rocks proves that the causes which produced them
were inticAaiely connected together. In the Krxgvbirge at
Oeicr the granite lnu forced itself up, in three blunt hills,
through the mica schist, which in its vicinity has been further
changed into gneiss ; and in the county of Cavan, in a similar
manner, rounded hills of granite occur amidst an ancient
UH-tam orphic schist. In the former case, the granite has
evidently been protruded subsequent to the deposition, and
even to the partial metamorphism of the schists, though the
exact epoch of protrusion is not determinable. In the granite
of the valley of the Neckar, near Heidelberg, though the exact
age cannot be settled, it is limited upwards, as the new rrd
sandstone, now partially removed by denudation, oner covered
the granite, and was therefore deposited subsequently to it ;
and such examples prove repeated action of elevating forces,
by which the surfree of the earth was disturbed and igneous
rocks protruded at various epochs. — Granite forms either
mountain masse*, or veins. Tbs veins are of various thick*
nes s es, from a km inches to several feet, and massive granite
k fr equent ly penetrated fay veins o i granite of a different
character, so that Leonhard designates the one, which U
read i e d porpbjritic by dkseminated fekpathk crystals,

n

MV DTM KWTAEY GEOLOGY.

tab granite; and the other, which is not porphyritic, vein
granite. When granite contains hornblende, it passes into
syenite, and by the passage of syenite into greenstone a con-
nection is established between ancient and modern eruptive
rocks. In the Odenwalder, syenite is traversed by many
granite veins, bat a vein of the syenite has not as yet been
observed in the granite, so that it is assumed that the syenite
is there older than the granite. Granolite or weisstein, in
which compact felspar it the principal constituent, has a
dote analogy to trachytes or fehpathic lavas ; it sometimes
assumes an independent massive form, and its veins traverse
granite. Yeina of granite, gnuiulite, and syenite often contain
large fragments of gneiss and other schistose rocks, which in
the vicinity of the masses from which the veins have proceeded
are both mod) contorted and greatly metamorphosed. • At
Meiasen and flohnstein, in Saxony, granite overlies the quarter-
•andstein, a result, it is supposed, of disturbance: at Chris-
tiania in Norway, and in the Harts, it is found between the
layers of primary schist and limestone, into which it has
penetrated by veins, changing the schists into a species of
horostone ; and many such examples might be cited from
similar districts. Greenstone, though it approximates to
granite by the intervention of syenite, is closely allied to
basalt, and forms therefore a connecting link between the
two groups ; but whilst granite and syenite afford only very
obscure examples of intercalation frith or superposition to
stratified deposits, greenstone is often so closely connected
with both the non - foemliferous crystalline schists and the
primary fosatliferous schists, occurring not only b intruded
masses and penetrating veins but also in beds alternating with
the regular strata, that Werner classed it with them, fichtstoae
beds penetrated by greenstone are often contorted in a similar
manner as by the action of decided igneous rocks ; and where
the greenstone and schists are disposed in regular and partM
strata, a distinct transition from one to the other mm fre-
quently be o b s e rve d , though in tome inrtances, especially
where them Is a thick bed of limestone* the separation between

* KUDfMKKTAlY GEOLOGY.

79

the two it very distinctly narked. It it thus that the more
decided metamorphic theorists consider greenstone an ultimate
result of metamorphitm, whilst the eruptive theorists connect
it with erupted rocks, and look upon its alternating bed* a*
the products of eo many distinct eruption*. In the neigh*
hour hood of Schwanenberg the mica schist it penetrated by
layers of greenstone more or leas parallel to the stratification j
and aa fragments of the adjacent rocks have been token op
by the greenstone, it has been suggested that the igneous
matter has been forced into fissures corresponding with the
natural lines of lamination of the strata. Some of these con-
formable dykes are more than 30 feet thick. This locality is
rich in ores, especially magnetic pyrites, iron pyrites, arsenical
pyrites, tin ore, black and brown blende, lead glance, and
stiver, and in simple minerals, — namely, garnrU, vrvuvtan,
chlorite, epidote, tourmaline, prase, mica, calcareous and
brown spar, and many others, the original composition of the
rock being almost concealed by the ore it contains. Granular
limestone ami dolomite are connected with the greenstone
here as in oilier localities.

Greenstone is characterised by k noil-like or conical masse*,
which are sometimes recognised at a distance as small lump-
like excrescences projecting above the stratified deposit, and a
columnar structure, though rare, is occasionally observed. The
dose resemblance between syenite end greenstone makes it
desirable to have some rules for distinguishing them i Cotta
gives the following —

Tto Avfc fJfNi fevfiMhfcfftrilG MmAmI
«n um w «■* L+ hnu * m-

•par m4 mmrtf tmgmtbm, hath

fMmiU, On 8— M u «r OnwS >w .
TW MSf «Hn 4 « wMhm

wmmv ISm IW 4 m% gram MM
•* OHM (*• crftufc at Um tat««r

e^n ■ — -* —

wvmnevsw MHOTi

Otmm, oppnmatmi ** Mxi
Irm fffUm m4 nw frtW y frU -
(UnfAi mO/tlmm

Caaim I.

S yw mttm.

Sum,.

XtJDIMXHTAJtY 6IOLOOY. "

Serpentine is allied to greenstone, and exhibits similar
physical features. Its veins penetrate the crystalline schist^
as well as granitic rocks, and it appears to have been
protruded amongst the beds of the Jura formation, being
abundant in the Alps. The well-known mixture of serpentine
veins in marble is a curious example of metamorphic action,
as it indicates diffusion rather than penetration, the veins
having no connection with any great mass. The fissures
and cavities of serpentine are often covered with asbestos.
Porphyry Group , including felspar porphyry, pitchstone por-
phyry, and augitc porphyry : rocks which ail affect a similar
physical character, appearing in lump-like masses and in dykes
projecting into granite, crystalline schists, and various stratified
deposits. They frequently appear as isolated hills amongst
other rocks, and hare been noticed in all parts of the earth.
Felspar porphyry, including horuatone and cUystone porphyry,
forms extensive masses, and also dykes of great length, which
frequently contain fragments of the rocks passed through, and
are sonfetimet bounded by a breccia formed by their attrition
against them. The }>crvading form of this group of porphyries
is rather angular than round, and as tabular beds and columns
are common, there is much analogy in structure to basalts
Metallic veins are rare in the porphyry, though more fre-
quent at its contact with schists. A remarkable example of
these rocks is seen in the Tharander Walde, where several
powerful dykes proceed in tangents rather than in radii, from
a round knoll more than a mile in diameter. The mam
mass lira between gneiss and day slate, and its dykes ramify
through both. At the Zeiaigstetnea it becomes columnar
and at the Eabcrge still more so, the overlying rock bring
quade rs a nd s tri n. Between Freiberg and Fraacastrin, dykes
many miles long cut through gneiss, and are the ms e lve s
penetrated by metallic veins. PUchstme porphyry, including
pitebstooe and pearistonc, is comparatively rare, and is usually
connect e d with other porphyries, which it either penetrates in
mam or by dykes: it oocurs in Saxony, in Hungary, and c*»

WO DIMK KTART GEOLOGY.

81

tensirdy in tbe island of Arran ; it appear* also in the felspar
porphyry district of Antrim. Mdapkyr (augitt porpAyry,
mugitc rock, $r.) is sometimes amygdaloidal, and generally
forms small knoll-like masses, or irregular dykes which pene-
trate massive and schistose rocks and effect important changes
in the fossiliferous deposits. There art many varieties of
this rock, and it becomes porphyritic from detached crystals
of augite, of mica, or of felspar. By its blsdder hkc and
amygdaloidal structure, and the occasional appearance of
columns, it approximates to basalts, and it has been rendered
remarkable by being in juxtaposition with masses of magnesian
limestone or dolomite, which Von Bucli supposed to have
been produced by a contemporaneous emanatiou from the
interior of the earth of magnesian vapours and their actum
on pre-existing limestone. The Basalt Group brings up the
working of ancient igneous forces to the very threshold of
the existing epoch. In basaltic countries, isolated conical
hills are common, and knob-like masses of all sues and
heights project above tbe surface of the country. Wing some-
times connected together in one great mass. Basalt is either
spread over other strata, like a stream of lava, or alternates
with them, having penetrated through both the ancient ig-
neous rocks and all the fossiliferous strata up to the post-
tertiary, some varieties intersecting others of more ancient
date. Where basaltic dykes have crossed other rocks, re-
markable chemical and mechanical effects have been pro-
duced 2 granite, gneiss and mica schist have been reddened,
and (especially the mica) partially melted \ day slate burnt
and hardened) sandstone redd en ed, glased, and reduced to
a columnar structure) stone and wood coal, charred) lime-
stone eometimee deprived of its carbonic add, and frequently
reduced from an earthy or compact to a crystalline state ;
shale changed to jasper ; fragments of underlying beds raised
to a higher level, mid the regular strata disturbed and upli ft ed,
though not to the same degree as by granite and porphyry,
the chemical oeadog the nechMncel tfftrti In this daaa

02

tVmilfTilT smoor.

of rock. PhmoUte (clinkstone and clinkstone porphyry) is
not oo widely spread as bamlt. Passages between clinkstone
and trachyte may be traced, and, where this rock occurs in
masses, the larger generally possess more of the trmchytic,
and the smaller of the phonolitic character. Columnar and
tabular forms of structure are observable as well ts dome-
shaped or conical hills. The trachytes which occur in the
well-known Siebengebirge, in Hungary, in the South of France,
and in the Andes, pass occasionally into phooolite, and on
the other hand varieties of phonoiitc are found associated
with basalt, Jxrre in its basaltic, greenstone -like, tr achy tic,
porphyritic, leucitic, and slag-like varieties, exhibits a cloae
analogy to other erupted rocks of all epochs.

Volcano** and Earthquake *. — In order to comprehend the
influence of volcanoes, which are the foci of eruption, as a
modifying geological force, it is necessary to bear in mind
that they are intimately connected with earthquakes, — the
earthquake often preceding the volcanic eruption, and both
being the result of the movement of matter in the interior of
the earth. It is thus that whilst the lavs which now flows
in streams over the sides of the crater, and the dykes which
penetrate its walls, are illustrations of the more ancient igneous
products, the movement of the earth's crust, its upheaval or
its depression, and the cracks which fissure it under the action
of earthquakes, or earth-waves, are squally illustrative of the
mechanical effects of former forces of s similar nature.

In thrgreat earthquake of Chili, 19th of November, 1822,
the shock was felt along the coast for 240 miles, snd by many
natural appearances, such as the exposure of beds of shells
at times of the tide when they were not before so exposed, it
was ascertained that at Valparaiso the uplifting amounted to
three, and at Quintero to four feet ; and as the great chain or
•xa of disturbance along which the volcanoes are arranged
is at a considerable distance, it is reasonable to suppose that
aB the intervening country was similarly raised. Thera ait
tram of more motet shocks which tore raised the ooaot

SDOIHlNTltT OlOiOOY.

81

•bout 50 feet. In the rocks of the const which are granite
and syenite, there are numerous parallel cracks which can
he followed landward for 1} mile. The effects of jin* earth*
quake extended over a space of J 00,000 square miles. An
earthquake shook violently part of Wallachia on the 11th
January, 1838 ; many parallel fissures were formed, and then
filled by matter forced upwards. The earthquake which
destroyed Lisbon, 1st November, 1755, was felt throughout
Europe so far as Norwiy, on the north coast of Africa,
in several of the West India Islands, and by many ships
at sea. At Lisbon, an adjacent hill was split in two, and
the new quay sunk 6(H) feet below tlie water. The changes
of level of the celebrated Temple of Puxxuoli, near Naples,
—the rising and sinking of the land in Scandinavia, — the
sudden appearance of islands forced up from below, — are
all phenomena which exhibit the still continuing action of
elevating forces. Jorullo, in Mexico, is an example of vol*
conic action combined with extensive elevation, and Skaptaar
Jokul, in Iceland, poured out a stream of lava which may
vie with many of the ancient basaltic streams — being about
50 miles long, 12 milrs wide, and on an average 100 feet thick.

The contemplation of such wonderful effects of still acting
cubes prepares us to estimate forces which acted according to
the same laws in former epochs. Whilst, therefore, water has
worn down, transported, and re-deposited mineral matter in
nearly regular and horixontal order, or, in other words, restored
the level of the earth's surface, that level has been disturbed
by the action of internal forces, which have elevated some
porticos of the surface above others. Elevation of the earth's
crust is necessarily accompanied by contortions and by cracks
varying according to peculiar circumstances j wberr, for ex*
ample, the derating force acta on a paint or small space, an
taolatrd mass or mountain may be formed with cracks radiating
frost a centre; or should the superficial pressur e be dimi-
nished, the crust may be raised like a great bubble, and, finally
separating at its apex, form the circular wall of what Von

84 BUOIMlNTAKt GEOLOGY.

Bach calls a crater of elevation : if it acts on the line of a
crack, either one side may be uplifted so as to form a steep
ptedpice overhanging a plain (an appearance not unusual in
nature), or both sides forming two precipices, with a valley
of elevation between them; and again, if upheaval takes place
where one set of cracks crosses others, there will be various
modifications of the primary ridges. Such forces, continuing
to set at intervals for ages, have produced the great and the
cross chains of mountains. Von Bucb, pursuing these inqui-
ries, observed that in certain districts the mountain chains,
the strike of the strata, and even the great ralleys, had certain
predominant directions; and Elie de Beaumont, extending
Von Buch's researches, founded upon them, in 1830, his
Theory of Elevation, according to which all mount mn chains
qf the earn* age have the eame general directum. Ilia Theory,
as now modified, may be thus stated ; that the earth's crust
has been elevated into mountains at various periods by forces
acting in the direction of great circles of the sphere ; and to
determine the relative ages of such upheavals, he assumes
that uplifted and highly inclined strata were deposited prior to
the upheaval winch disturbed them, and that horizontal strata
which overlie the inclined or disturbed must have been deposited
subsequently to such upheaval ; and hence that the epocB of
deration may be determined by tbe relations of successive
sedimentary deposits to each oilier. M. Elie de Beaumont at
first distinguished about fifteen systems of elevation, of which
the twdvadollowing are the moat remarkable.

1. System qf Westmoreland and UunsdrUeA . — Direction of
deration, w. s. 4 s. and a. w. 4 w. No newer strata than
the Silurian, and probably a part of Devonian, uplifted. This
indudes the Eifcl, the Taunos, the Isle of Man, and 8outh
Shetland. 2. System qf part ef the Tange*. — Direction, n.
15° s., w. 15° a. Mountain limestone, but not the ooei-
beartng strata, uplifted. To this belong the hills of B ocage,
b Calvados. 3. 8yi*m qfth* North Direction,

a. — n. The coal-bearing strata are the meet recent aJfccted

ru dim Bier ary geology. gg

in this elevation. 4. System of the Netherlands and of South
Wales, — Direction, n. b. — s. w. The whole of the coal
formation affected. 5. System of the Rhine. — • Direction,
— n. or s. a. ye. — n. n. b. Strata to the Zechatein
(magnesian limestone) uplifted. The Vo*ges, Schwarswald.
6. System of Bohemian and Thuringian Forests. — Direction,
s. k. — w. w. The keuper is the newest formation disturbed.
La Vendee, Bretagne. 7. System of the Eregehirges. — Direc-
tion, a. w. — w. b. The oolite or Jura, but not the qttader*
eandtteiu, affected. CAte d'Or, Mount Pilas and the Jura in
part. 8. System of Monte Viso. — Direction, n. n. w.—
a. a. B. The older but not the newer chalk affected. 9. Sye*
tern of the Pyrenees and Apennines. — Direction, ic.w. — a. a.
The younger or upper chalk, but not the tertiary strata, af-
fected. This system being parallel to No. 6, it is often difficult
to separate one from the other. Harts, Teutoburger Forest,
Ac. 10. System if Corsica and Sardinia. — Direction, S. — W.
The lower tertiarics, but not the upper, affected. The basalt
of Hesse. 1 1. System of the Western Alps. — Direction, w.
26° b. — s. 26° w. The newer terttarics affected. 12. System
of the main chain of the Alps : from Wales to Austria . ~
Direction, w. — b. or a. it. b. — w. a. w. A portion of the
post-tertian c* affected. Monte Ventoux, Le heron.

M. Elte de Beaumont has since extended his determination
to at least twenty-one systems of mountains, the relative ages
of which have been determined with more or less precision,—
namely, the systems of La VendiSe, of FinisUre, of Longmynd,
of Morbihan, of Hands rOck, of the Ballons, of Foret, of the
North of England, of the Low Countries, of the Rhine, of
Thffiingerwald, of the €6te d'Or, of Monte Viso, of the Pyre-
nees, of Tatra, of Sanertroia, of the Western Alps, of the
main chain of the Alps, of Tenare and of Vercors ; and M,
Dumber has pointed out several other systems in Scandinavia.
The difficulty in determining the actual connection of a chain
of mountains with aome definite system is sometimes great, m
ffisturbenm and e l ev a tion s treqat atfy occur in the same die*

ftVDIVtirrAtT GEOLOGY

86

trict and nearly in the tame direction. This periodic recur*
race of pulsations, as it were, of the earth's crust in particular
districts, rather than indefinitely over the whole surface, has
led M. dc Beaumont to inquire whether the various systems of
mountains resulting from the action of some central force, and
therefore necessarily exhibited in great circlet on the surface,
may not be reduced to some geometric law ; and the result of
his investigation is, that the phenomena may be best exhibited
by dividing the surface of the sphere or earth into twelve
regular spherical pentagons produced by the intersections of
fifteen great circles. The various systems of mountains may
tbqn be arranged around the angles of the pentagons, and be
considered as produced by disturbances acting in auxiliary
great circles passing through the angles of the pentagon and
forming so many bulging or even geometric projections (like the
boas of a shield) of which the angles of the primary pentagons
are the apices.

'Whatever opinion may be formed of the details of M.
Brongniart's theories, in their groundwork they are correct,
and they have had and will have a most powerful effect on
the progress of geological science.

The fact has thus been established, that at sucoearive
epochs the earth's crust has been broken up and elevated,
whilst various igneous rocks, the most superficial of which was
probably granite, were lifted up and forced into the cracks of
the disturbed crust ; hut the mode in which the great elevating
force has been developed has yet to be investigated, and here
indeed is a difficulty, as direct observation can only extend to
a mere film of that earth the surface of which it has affected
in to striking a manner. The frets, however, of disturbance
are palpable, and the nature even of the forces producing them
can he in fe rre d , though not demonstrated by observation.
Electricity may he fairly clamed with them forces, if only as a
secondary cause ; and it may be attained on w ida t reasons
that heat was a primary oaa. la 1837 Gustav Bmcbof
a fiuid condition of the central portions of the earth

XVMMKKTAKY GEOLOGY.

87

from heat, flood from phvaioal considerations deduced that hot
springs, the production of massive rocks from the cooling of
the fluid mineral matter, volcanic eruptions and earthquakes
consequent on the expansive force of steam produced by eon-
tact of water with the still heated and fluid internal mass, were
the results of such s condition.

Sir H. Davy proposed s chemical theory of earthquakes,
founded on the properties of the newly discovered buses of
the alkalis and earths. These bodies, when brought in contact
with air and water, arc oxydated with great rapidity, producing
an intense ignition : he therefore considered it proltablc that
potassium, sodium, calcium, Ac. exist in great quantity in the
interior of the earth, and coming into contact with water
which had penetrated by cracks or filtration, is suddenly
ignited and oxydated, giving rise to volcanic fires and to the
formation of various stony compounds, which, as larms, are
then erupted. The great quantity of sodium in combination
with chlorine, iodine, and bromine in sea water and in salt
deposits indicates that this cause must not be entirely rejected
in accounting for local phenomena, though it is insufficient
to account for the more general phenomena of disturbance.

The theory of Cordicr is purely thermometries!, and is very
generally adopted by Geologists: it msy be expressed under
the following heads :

1. The earth has an internal temperature, which is in*
dependent of the solar beat, and increases rapidly with tbfl
depth.

2. The rate of augmentation ts different at different places ;
in one country it may be double that of another, and the
difference is moi in a constant ratio with either latitude or
longitude.

3. As the total mesa of the earth is shoot 10,000 times
greater than that of the waters connected with it, it is more
probable that the origiasl fluidity of the earth was due to heat
than to aqueous solutioa, The heat was very great, as (he
present temperature at the eaotrs of the earth, flupp ofli n g a

68

ftVBIMBKTAEY GEOLOGY.

regular progression in the increase downwards, exceeds 3500
of Wedgewood’s pyrometer as 450,000° Fahrenheit.

4. A temperature of upwards of 12,000° Fahrenheit, which
is sufficient to melt most of the known rocks, would exist
at depths below the surface varying from 60 to 160 miles,
supposing the increase to be regularly progressive ; but it is
highly probable that the dense fluid portions of the earth are
much better conductors of heat than the crust, and therefore
that this high melting temperature is acquired, and that the
actual fluid portion commences at a still less depth.

5. As the crust of the earth, letting out of consideration
aedimentary deposits, has been consolidated by cooling, ita
formation must hate taken place from without inwards, so
that the more superficial crystalline rocks are the most ancient ;
and this accords well with the small density of granite which
appears to bate been uplifted under so small a comparative
pressure as not to hate been actually erupted. Tlie thickness
of the crust will continue to increase until the cooling has
attained its final limits.

6. There is no reason for believing that the solid crust can
be more than from 60 to 100 miles thick, and it is probably
much less : that it is very unequal, is shown by the variation
of internal temperature, which cannot be explained by different
conductibility alone. It possesses some degree of flexibility,
and the phenomena of earthquakes are due to the expansive
force and consequent pressure which the fluid nucleus within
exercises upon it.

7. The solid crust continues to contract as its temperature
diminishes in a greater ratio than the central mass ; and as the
velocity of rotation must increase as the diameter of the planet
diminishes, there will be a tendency to diverge further Arose
the spherical form, and hence the fluid matter within will
press against the contracting crust, and produce volcanic
eruptions. M. Cordier has calculated that a contraction of
nin °f on inch in the mean radios of the earth wosaki
be sufficing to force out the matter at a volcanic cruptioo.

KVDXMKRTAtT O BO LOOT.

99

In this hypothesis, the tones of least thickness of the earth
most be the sites of volcanoes. Professor Rogers, of Phila-
delphia, has traced the progress of three great earthquakes
in the United States, the synchronous lines of which, or lines
along which the shock was felt at the same moment, extended
300 miles in a direction from n. e. to a. w the progressive
motion being to the eastward, at the rate of 30 miles a minute.
It is highly probable that elcetric forces called into action
by change of temperature have aided in the production of
these effects, and that partial differences in the conductibility
of different strata have increased or diminished the intensity
of earthquake shocks or waves, and by producing local cracks
have been one of the causes of the various subterranean noises
which accompany these great and fearful phenomena.

It may he added that M. llozct, by comparing a series
of pendulum experiments with the geodetic measurements in
France and with barometric observations, has proved that
lofty mountain chains are not the only evidences of the dis-
turbance of the crust, but on the contrary, that the apparently
level surface of the earth conceals many undulations which,
by their effects on the pendulum, have evidently been pro-
duced by the swelling up of denser matter within them.
M. Hotel has further established the fact that the ocean has
not, as so many English Geologists imagine, an invariable level,
but participates in the movements, and conforms itself to the
varying level of the solid crust. u We find.” he says, •* that
the true level of the ocean is below the mean elliptic level in
tbe Polar Sea, on the coasts of Spitsbergen snd Greenland, as
also on the coasts of Great Britain, at the Equator, and in the
Southern Ocean, and that it is above that level on the coasts of
Norway and at the Cape of Good Hope/* This inequality of
absolute level in the ocean, consequent on the protuberances
mid hollows of the crust of the earth, must have varied with,
and been in proportion to, every great disturbance, or to the
amount of matter protruded above tbe mean elliptical level of
the liquid nucleus. By the c al cn k ti on s of M. Rend, the mm

00

ftcstMiirrm geology.

of the Alps, if entirely composed of basalt, should deflect the
plus»b< lint only whereas on the eastern flank of these

mountains the deflection amounts to 28", and on Mount Ccnie
itself to 8" -5 ; whence it is concluded that this great deflection
is due not merely to the mountain itself, hut to the denser
matter proceeding from the interior of the earth, which had
been forced into the protuberance, on the summit of which the
mountain chain rests. It is not therefore the sedimentary de-
posits alone which hare acquired an irregularity of surface;
the general form of the earth has been altered from its original
condition, not by one but by many successive commotions,
and as the thickness of the solidified crust has continued to
increase, the most recent chains of mountains are necessarily
the most elevated.

The violent intrusion of igneous matter either into cracks of
the crystalline portion of the earth's crust or amongst the
more purely sedimentary strata must tend to crush, consoli-
date, and contort the strata, and, wherever the crust has been
rent asunder, to produce s jar or vibration of the solid matter,
which jar is transmitted like the vibrations of sound through
the solid crust, ami constitutes an earth-quake or wave. This
theory of Young and Gay Lutaar has been lately moat
admirably worked out by Mr. Mailed in hit Keports to the
British Association. It is highly probable tint in some eases
the igneous matter injected from below and the wave of the
solid matter has only affected the luwrr strata, which have
been contorted, whilst the beds above them have remained
apparently unaffected by the disturbance. In such easts these
would be an apparent but not a real want of ceoformabiliiy*
In other cases igneous matter may be forced to the surface, as
in volcanoes, and comparatively little jar or earthquake pro-
duced. In the theory of Cordier, the central nucleus of the
earth is considered a liquid of ignition, hut it has been urged
that the great pressure would retain it in a solid state: t(
however, such bribe case, wherever the pr ess ur e was relieved
the matter would become locally liquid, and thus agree with

IWWtKTAlf QIOIOOT. f f

the opinion of Mr. Hopkins, that there is not a nnirersal
central let of molten mineral matter, but local lakes from
which volcanic rents are supplied. These two theories are
therefore reducible to one. To the probable influence of elec-
tricity should also be added that of magnetism, as the beautifW
d i scov e ries of Mr. Faraday have made it easy to connect it
with great physical phenomena. All bodies are either para-
magnetic or diamagnetic, that is, they are either in a state
of magnetic attraction or of repulsion : if, therefore, a change
in theae conditions be brought about by any agency, whether
h be heat or electricity, the cohesion of matter will suddenly
cease in one place and at another He called into action, giving
rise to violent disturbances even in the solid matter of the
earth.

Practical Application*. — The practical importance of metm-
morphic, pi u tonic, and volcanic rocks requires a brief notice.
Tk * metamorphic includes those varieties of clay slale which
are used as roofiug slates , and the physical condition of the
strata is therefore a guide in searching for slates, as their
peculiarities and value are due to metamorphic action. The
lesser cleavage of the slate is usually transverse to the dip of
the beds ; and the probable value of the slaty beds may be
estimated by the presence or absence of this character, as the
planes of separation by cleavage are more regular, and (masese
a more even surface than those of strstiftrattmi. For flagging,
many crystalline schists are excellent, as the surface of strati*
flection is suflictmtiv even in the gnetsose varieties of mica
slate and in gneiss ; and they also often furnish good rough
building stones, affording a flat bedding and a my durable
composition. In these three varieties of metamorphic schists
the important physical character of specific gravity is nearly
uniform, as it ranges in each from about 2 6 to 3 1, which k
the speciflc gravity of the more dense or indurated varieties
which am frequently hornblende or greenstone schists. At
road stones, the letter only should be used, es other varieties
speedfly break up and art reduced to mud. Booing sluts*

n

fttJDmXffTAEY OBOLOGY.

ought to split thin and even, but should neither clem into
fragments nor break off in scales ; they should not absorb
much water, as it induces the growth of moss, which speedily
disfigures them and produces damp. Though the dark grey
varieties are most approved, the silver grey arc usually the moat
durable. Some varieties of mica slate afford good roofing
slates, which, however, are seldom so thin and even as the
less crystalline schists. Wales is the most important locality
of the United Kingdom, but there are very good slates in the
South-west and in the 8outh of Ireland, at at Killaloe on the
Shannon, and in the island of Valentia, and some from the
tnica alate of the North of Ireland though they are inferior to
the true alates. Of foreign localities, that of Lehesten in the
Thuringian Forest may be mentioned.

Wbcu mica alate and gneiss are used as building stones,
gneiss, or highly gneisose varieties of mica alate, should be
selected for situatiotis exposed to much wet, as the finer
grained, or more slaty varieties, rapidly disintegrate ; but
where the building or any of its parts are likely to be ex-
posed to much heat, as in the sides of chimneys and fire-
places, the true mica schists, or the fine-grained varieties, are
preferable. The city of Freiberg is built of gneiss, and its
streets paved with the tame material.

The most important of the pi* tome and rolcanie roch art,
granite, syenite, porphyry, greenstone, basalt. Many varie-
ties of granite are excellent as building stones, though expen-
sive in working to definite forms. Some of the most impor-
tant public works of Great Britain and Ireland, France, and
Russia (Petersburg), are of this material. In selecting gra-
nite, those varieties in which the constituent minerals are very
small and the scales of mica superabundant should be avoided;
and as a practical test it is wise to notice the country imme-
diately around the quarry, as the wady varieties rapidly dis-
integrate, and form accumulations of micaceous sand. The
llayter or Dartmoor granite, ths Aberdeen granite, the Kings-
ton (Dublin) granite, tome beds of the Mom or county of

RUDIMENTARY GEOLOGY* 93

Down granite, and the Guernsey or Channel Island granite,
are well known for their excellence. In some of the quarries
the bedding of the granite is more defined titan in others;
and wherever this is the case, or where marked cleavages or
joints prevail, the working is much facilitated. Many old
Egyptian works and statues were formed of granite, and it is
still used for colossal works, as it takes a fine polish : for
example, the great fuuntaiu shell or vase before the Museum
at Berlin, and the pedestal of the statue of Peter the Great
at St. Petersburg, are of Northern granite, being sculptured
from erratic blocks. The splendid Scotch granite columns in
the vestibule of the PiUwilliam Museum at Cambridge arc
beautiful examples of a modem application of this rock to the
arts. Millstones are occasionally manufactured of granite.
As a nun] stone, those varieties which have at once a fine*
grained ami a close firm texture should be preferred, as the
Urge crystals of coarser granite are liable to cleave into frag«
ments. The specific gravity of this important stone varies
from 2*6 to 2*6, which is very' analogous to that of the meta-
morpbtc schists, — a circumstance which gives weight to Keil-
linu's opinion that in many cases it is a mctamorphic and not
an eruptive rock. Syenite is even a firmer stone than granite,
and its specific gravity, which ranges from 2*6 so high as 3*0,
approximates it to greenstone. Many beautiful varieties of
this rock are found in Ireland. In Dresden, syenite is hewn
into regular parellelopipcd blocks for {taring, a purpose for
which its durability and firmness peculiarly fit it ; and as a
mad stone generally it is excellent. Many ancient Eastern
works were formed of it, and from its tenacity large objects
have been fashiooed not of single blocks.

PorpJkyty. — This term has an extensive application, as it
may be used in reference to any rock in which isolated crystals,
usually of felspar, are imbedded in a distinct paste. As a
building stone, all thoae varieties baring a soft argillaceous
pasta must be rejected ; but them are many which afford
good rough building stones, and also good road st on es, aaaQy

•4

ftTJDIMKVTiKT GSOLOGY.

breaking bin proper form* and sixes, binding well, keeping
dry, and being tolerably fret from dost, — a consideration too
little attended to in the selection of road stones. Fran the
beauty of its colours, some varieties of this rock bare been
largely used for columns, monuments, and rases. The red,
brown, black, and g reen antique porphyries are well known to
the student of ancient art. The red porphyry. of the ancients
is composed of a felspathic paste of a violet-red or wine-red
colour haring small crystals of black hornblende and grains of
specular iron disseminated through the mass, and isolated
crystals of a rose-red felspar. The paste contains 62 per cent,
of silica, the isolated crystals 69. The crystals contain nearly
8 per cent, of soda and potash, of which only \ is potash; the
paste 6 per cent., of which | is potash. The paste is very rich
in magnesia, the proportion being so high as 6 per cent. ; in the
crystals it is less than 2 per cent. This porphyry is distin-
guished from that of KUdal by a lesser proportion of silica and
a greater specific gravity, the quantities being thus : Red por-
phyry, silica 64; specific gravity 2763: Eifdal porphyry,
silica 76 ; specific gravity 2 623. It is to this excess of silica
that the superior hardness of the Eifdal porphyry may be
ascribed ; and, aa M . Delesar observes, the density of the por-
phyry may be, considered an index of the quantity of its silica
and consequently of its hardness. In modem times, the most
remarkable porphyry works are at Eifdal, in Sweden, and
Kolyma, in Siberia. The Eifdal works have been established
about sixty years ; they are in the province of Dalarne, amidst
wooded mountains, and in a wild country. The blocks are
worked into form and polished by well-adjusted machinery ;
and most beautiful works of art as columns, vases, chimney
ornaments, and tables, are produced, rivalling the ro ea o antico ,
or aaasnt red porphyry. A magnificent vast of this porphyry,
at the country palace of Johanasthai, is 10 feet high, and at
its summit 16 feet in diameter : it rests on a base of granite.
The principal ddpM of this manafeoture is Stockholm. In
tha wo rks h ops of Kolyma* in Siberia, equally bmitf iftil qpeci-

ivNumav otoLoeY.

M

mens of art are ma n uf a ctu red, and forwarded in large quan-
tities to St. IWrsburg. The block* arc sometimes of great
sbe, 900 mm bring employed to draw a angle block. Some
of the porphyries of Hungary resemble the grey porphyry,
the mordighone of Roman artist*. The specific gravity of
porphyry varies from 2** I to 2*$, and it may be observed that
tbe beautiful polish it take* is a prinajud cau*r of it* extreme
durability ; many work* formed of it remaiumg uuiujured for
age* amongst tike ruin* surrounding them.

Grtentfomt . — The specific gravity of this rook ranges from
2*7 to 3*0, and though it* extreme hardness, ami the difficulty
of clearing it without spliutrrs, render it less fitted for regular
buildings, it may be u«ed with advantage as a rough building
stone, and for a road stone is ncellent. The porfido verde-
antico, or green porphyry of the ancients, noticed under por-
phyry, is a greenstone porphyry, the base bring greenstone,
with white and green isolated crystals of felspar. The Corsican
globe rock is a compact greenstone with globular concretions.

Bmsmit — This rock, so remarkable for the columnar struc-
ture so beautifully exhibited by many of its beds, a* at Staffs
and the Giant's Causeway (see alto fig. 17), has a high
specific gravity, varying from to 3* 1. In the more dense
varieties its very great hardness makes it difficult of use for
squared work ; but for rough building, and especially for sea
walls exposed to much w tar, it is excellent. For paring
■tones it would also be admirable, were it not that tbe sur-
fee becomes polished and slippery ; but as a road stone it
cannot be excelled, making at once a firm, durable, and dip
road. Though not common, some of tbe aphynxes and hone
of the Egyptians were formed of baealt. Trachyte and the
trachytic or fekpathie lavas, and the various other products of
ancient and modem volcanoes, naturally come into this see*
tion. In the county of Antrim largely, and in the county of
Down in email quantity, tiunbytas porphyry bee been found,
summing In Antrim a column a r s tru c tur e. It appears also to
be a product of the wil m ulr districts of New Z e aland, It

ETTDDfKJVTAfcY GEOLOGY.

M

forms t handsome and durable budding stone. Of other
km products, soch as tufa, the Romans used them extra-
rfvely, as is observed in the rains of Pompeii : when poro us ,
they are very light, and may therefore be often applied with
advantage where that quality, combined with strength, is of
importance: their absorbent quality renders walls lined with
them very dry.

Opkioiiie or Serpentine . — The mineral ‘serpentine,’ by
which name a massive and comparatively impure rock is also
designated, is a bUilieste of magnesia, and has been well
known from the earliest times. In all parts of the world,
Some of its varieties have been used in the formation of
images for idol worship, and in the manufacture of rases,
columns, pipes, he. The rich green and bronxe tints of its
finer varieties, and the high polish of which they are sus-
ceptible, render it highly ornamental and valuable, and in
Saxony it is still extensively worked. When reining carbonate
of lime, it becomes the ophicalce of Brongniart, of which the
green marble of Galway is an example ; when porphyritk, it
it his ophite.

Li met tone . — It is associated with other metamorphic rocks
hi a manner which deserves especial attention. It is inter-
stratified with mica schist, in layers varying in thickness from
a mere film to beds several feet thick, and exhibiting the
metamorphic change by a highly crystalline structure. When
the crystals are not too large, it becomes a granular marble,
and wheif veined, as in the county of Galway, with g reen
terpentine, forms a verde-antko. Such marbles as these,
including the finest statuary marble, which were formerly
called primitive limestooee, are of various ages; the marble
here noticed, and that of Donegal, belonging to metamorphic
racks of a remote epoch, whereas that of Carrara b compara-
tively reoent In metamorphic districts, soch as the mica
achist country of Deny, Donegal, Scotland, 4c., this Hirst ons
i a raso urae for time, but it is impoemhle to notice its
r scale of its <

lcoratiiTitf oaobocnr. 17

at compared with the voontib Kmwte B i of the carboniferous
tad the chalk of tha cw to M W i systems, without ptrta t f tof
that argiDecrooa or muddy deposits there predo mi nated,

Mtimlh c Depamts.—ln Europe the plutooie and metamor-
phic rocks are tha great dcp6ts of metallic ora; and In Booth
America, though gneiss is less productive and tha oraa con-
tinue into the overling strata, it is highly probable that tha
latter hare also been subject to metamorphic action, and that
metallic reins hare been connected in them, as in the crystal*
line schists, with electric phenomena.

Iran. — English iron is obtained from an ore not connected
with metamorphic strata, which will be noticed in its proper
place ; but the celebrated Swedish iron is procured from map*
nctic iron ore connected with rocks of this class, and forming
mountain masses in Tsbcrg, in Smoiand. This ore occurs in
beds which sometimes alternate with the metamorphic strata
at Dannemora, and various other places in Sweden, Norway,
Russia, Ac., and it has also been found associated with plu-
tome and volcanic rocks. The frr ohgiate, specular or Elba
iron ore, sometimes replaces mica in mica schist, and is asso-
ciated with adularia at St Gothard. The peroxide of iron
forms reins and beds in these rocks, though it is also found,
as well aa the other ores of iron, in other deposits. Many a-
siw — Its peroxide has been found in metamorphic rocks, hut
it belongs more especially to sedimentary deposits.

Capper . — Copper pyrites, or bisulphurrt of copper and iroi^
the most important of copper ores, occurs principally on the
Continent in gneiss and mica schist ; in Cornwall, and in the
south of Ireland, in varieties of clay slats ; in tbs Harts in
similar strata (or the old grtuwackc); and in Tuscany at
the junction of serpentine trapp (gahbro) with tha tertiary
strata. This mineral occurs also in the bituminous or copper
schist (kupfmduder), a portion of the lecbatcin, magnesian
limestone, or Penman formation, la the Oural mountaina,
in Siberia, the double sulpboM of iron and copper is (lit,
and is replaced by the simple snlphuret of copper, the strata

M EUDIMEWTAJtY GEOLOGY.

being probably sedimentary : tins ore occurs also in the por-
phyritic district of Tyrone . The other ores of copper do not
here require s practical notice.

Lead. — Galena, or bisnlphoret of lead, occurs in pfatonic,
metamorphic, and foniliferous sedimentary deposits.

Silver . — Bisulphuret of silver, the most important of its
ores, has been found in gneiss and mica schist and in their
associated limestone, in greenstone slate, da y slate, syenite,
and porphyritic greenstone. It extends up to the xechstrin;
but it should be here observed, that in some of these cases, as
in Mexico and Peru, the veins run from the metamorphic to
the ordinary sedimentary deposits, and have therefore been
manifestly connected with the cause of metamorphic action.

7 Y*. — Binoxide (deutoxide) is the most important ore. In
Cornwall, the great source of British tin and the most im-
portant one in the world, the ore occurs in granite, and also in
killas, a partially metamorphic schist ; and in other parts of
the world, in granite, in metamorphic schista, or in porphyry,
or porphyritic schists of the secondary class. Like gold, it is
also worked as stream tin in sands proceeding from the disin-
tegration of the tin-hearing rocks. Zinc. — Bisulphuret, usually
associated with bisulphuret of lead. The carbonate belongs to
Tarioui mineral deposits, extending even to the tertiary.

Mercury especially belongs to primary and secondary fas-
sihferous strata, though it is found occasionally in mica schist or
crystalline metamorphic rocks, and in Haute -Vienne dispersed
in globules in granite. The rich ore of mercury, cinnabar, of
Airaadcu in Spain, it procured from grauwacke (primary)
strata, and has been worked for ages.

Antimony , — Bisulphuret of antimony b rare, and found in
veins traversing granite, gneiss, and mica schist. Moiybdmuu
— The btsulphtirct b found generally, in small misses, in
granite and mica schist, and occariooaUy associated, though
sparingly, with ores of tin, as in Cornwall, he., and srilPmora
rarely with copper pyrites, as in Norway.

OeU ha a bean found in Brasil disarm mated in c o na i dtirahk

ivmvtirrARt otology.

!>9

quantity in qwr t w e and chloritk* rocks, which belong to the
metamorphic system ; and auriferous sands, which contain
also platinum and diamonds, arc the result of the decompo-
sition of such rocks. Gold has in other places been found
in reins tr a ver si ng metamorphic rocks, from which the Wick-
low gold sands hare proceeded ; and indeed the greater pro-
portion of gold is obtained by washing from auriferous sands.
Gold is very widely diffused in Nature, though usually in
small quantities. lu Russia the ralue of gold obtained from
the Oura) mountains amounts annually to about three millions
sterling ; hut that procured from the New World exceeds
greatly eren this large return. Independently of the old
mines of South America and those of the southern portion of
the United States, California furnished to the Philadelphia
Mint in )H50*ix and a half millions sterling of gold,— a quan-
tity which probably exceed* that furnished by the rest of the
world. An announcement has also been made in the public
journals of the recent discovery of valuable gold mines in
Australia. Pfatmwm is associated with gold in the auriferous
sands of Brazil, of Russia, and of Wicklow in Ireland ; it has
also been discovered in Prance.

This genera] occurrence of metallic ores in rocks which have
undergone a metamorphic rhangr, though at very various
epochs, their occurrence in veins, and the fact* observed by
Mr. Pox of the conduction of electricity by mineral veins, and
the development of metals and minerals near the contact of
highly metamorphic strata, stated by Krilhau, are strong
reasons for ascribing their presence under such circumstances
to an electric cause.

V fin — As the term vein ocron frequently in this section,
it is desirable to explain it. The idea which the word con-
veys is distinguished from that of dykes, as it implies a
waving rather than a rectilineal course ; but this distinction is
wot always preserved, as many veins, and particularly metallic
lodes, are rectilinear. Veins may, bowerer, be placed in two
saetions * namely, those which, unconnected with any great

100

KomnrntT geology.

extraneous man of matter, originate m and are confined to
tl»e rock in which they occur, and thoae which spring from
and are connected with tome great extraneous mass. The
first may he found in all rocks, are often so fine as to be
quite capillary, and frequently intersect each other) forming a
complete net-work t they are considered reins of segrega-
tion, haring been probably cracks into which the crystalline
matter now filling them has been gradually removed from
the surrounding mass. They consist sometimes of quarts,
and sometimes of carbonate of lime. The others are often
connected with large masses of external rock, the matter of
which is identical with that of the reins ; and it has therefore
been very generally assumed that such reins are reins of in-
trusion, though by Keilhau they are considered an advanced
product of metamorphic action. Where metallic veins pass
through various strata, the sedimentary included, they have
most probably originated in cracks consequent on disturbing
movements from below, ami hare been filled partly by segre-
gation, modified as to its results by electric currents, partly by
sublimation, partly by the decomposition of volatile per-
chknrides, fluorides, and borides which have permeated the
earth’s crust through such channels, and partly by infiltration.
Home of these reins are of great magnitude, an example of
which may be cited in the great ironstone rein of the red
mountain near Schwarxmberg, which is between 40 and 50
feet thick/ and stretching along the boundary between the
granite and gneiss (partly in the gneiss itself) has been traced
for about four miles.

CHAPTEK V.

famBi — patrifreti— i c — d kk a s of futiM Bsdks, mi Minks

PcftrttMtka — Pstrtfytaf Ub*m*m Dktrftalkw af HmB*.

Tat term fossil, in Ha original and natural sense, might be
applied, as H formerly waa, to any body dug out of the earth.

ftVDIMKHTABY OlOtXMTT.

101

tod would the© c omp rise minerals, metals, tod tU other sub-
stances that obtained. Amongst such fossils thm tfi ooot-
siooaDy found mmenl bodies which exhibited to strong t
resemblance in their external forma to known organic struc-
tures, that it was impossible not to aak — art thee* bodies
merely the production of some fanciful operation of Nature**
powers, or sre they really relict of organised beings! The
progress of discovery soon led to the rejection of the first of
these theories, and for a time geologists, deceived by s general
resemblance and overlooking the specific distinction between
fossil slid existing organisms, explained the occurrence of or*
ganic fossils within the solid matter of the earth by the
operation of the great Deluge, which they supposed to have
torn op the crust of the earth and spread its comminuted
fragments over the so Hare mixed up with shells and other
organic bodies which were living at the time of the great
catastrophe. The labours of modem philosophers have dis-
jxrllcd this second error, and established a new science.
Palaeontology (doctrine of ancient or extinct animals), by
discovering that fossil organic bodies sre specifically and often
gcoencallr distinct from any now living, and are therefore, as
relics of extinct animals, the records of successive phenomena
which involve the appearance and disappearance of organic
bodies, under forms and combinations suited to the varying
conditions of the earth's surface.

The weight of this evidence in favour of the existence
of assemblages of animals and plants, which at successive
epochs of the earth's history have been swept awsy, may
be estimated from the fact that probably nearly 30,000 spears
of fossil animals and plants have been discovered and de-
scribed , s number which is very great, for though more
than 170,000 existing animals and plants are known to
Naturalists, it must be remembered that very many of them
belong to clas se s representatives of which, either from the
nature of their habitation or from the soft and perishable
character of their bodies, cannot be expected to be found

102

EH D1ME9TAEY GEOLOGY.

itt a fossil state. Of the number of plants which have thus
Ulred at ancient epochs and passed away, some idea may be
formed from the rich collection of Gogppert, author of ‘La •
Genres des Plantes Fossilea,’ Ac., which contains more than
3000 specimens of vegetable petrifactions ; namely, 236 from
Cambrian and Silurian strata, 1348 from the carboniferous,
93 from the trims or new ml sandstone, 61 from the lias
and oolite, 242 from the green- sand, chalk, and gypsum,
742 from lignite*, 259 of unknown localities, and 50 of recent
forma, which occur in three condition*.

1 . Stem*, leaves, 6owm, fruits, interposed between layer*
of stony or earthy matter, and either slightly browned, or in
various states (up to the most perfect) of carbonisation.

2. Impressions of the hark of plants, the interior of which
is either empty or filled with stony matter.

3. Complete petrifactions, in which the whole of the interior
mass, as the several organs, cells, and vessels of the plant,
are filled with stony matter, and not, as is commonly said,
changed into stone.

M. Gocppcrt illustrates the first by experimental imitations
of the distribution of fossil plants in shales and grits. Living
plants, particularly ferns, werr placed between layers of
soft clav, which wen* then dried in the shade, and after-
wards exposed to heat varying in intensity up to a red heat.
Accunliug to the degree of heat, the plants were found either
•lightly hfowned or perfectly carbouixrd ; and when either
powdered coal or asphahe had been mixed with the day,
they exhibited a shining black tint, and adhered to the
layer of clay. When the heat had been pushed to redness,
and the plants were entirely cousumrd, impressions of both
faces were found, just as in the grits of Silesia. In the second
experiment, the plants were placed between layers of day, and
were left immersed six feet deep in a ditch for a whole year,
when they were more or less browned (as plants are when
naturally immersed in the mire at the bottom of ponds), and
might have been mistaken for the impressions of fossil plants.

KUDWXXTAlt OXOLOCHT. 109

la ths second condition, which hat not been ftdly illustrated
by experiment, the berk of the plant* som e t im e s remains end
resembles coni, whilst ell its external peculiarities ere impressed
on the enxroandmg matrix, and the mar kings of the internal
surface are exhibited on the atony oast formed within it ; no
that in auch cases the cast and the mould hare frequently
been taken for different bodies. Sometimes the hark is re-
duced to a film of coaly powder between the impression of the
mould and the cast ; and as the decomposition of the thin bark
of such plants preceded the formation of the cast, the impres-
sion of the mould corresponds at once to the original external
surface of the plant, and to that of the cast. When decom-
position and petrifaction hare taken place under pressure, the
stems are more or lees flattened ; and in some calamites the
opposite surfaces hare been pressed close together, the whole
internal substance haring been rrmored before the consoli-
dation of the surrounding mass had secured it from the effect
of pressure.

In the third condition, mineral matter lias been infiltrated
into and lias solidified within the interstices of the cells and
r easel*, the walls of which hare been more or less preserved.
In vegetable fossils the ordinary petrifying substances are
•ilka, carbonate and sulphate of lime which are soluble
in water, peroxide of iron, smooth clay, or a mixture of
several of thrse ingredients ; tud M, Go^ppert proves that
the process is still going forward, by specimens of oak
received from M. Cotta and from ML Laspe, which were
taken from a brook, and having been fossilised by car-
bonate of lime are hard enough to take a fine polish,
the vessels and cells, excepting some of the medullary rays,
being entirely filled with carbonate of lime. In a specimen
of wood from a Homan aqueduct, petrifaction is confined to
cylindrical spaces traversing the ligneous structure longitudi-
nally, which were probably vacant spaces produced by decom-
position and filled up by stony matter. The wood surrounding
the petrified portions is perfectly sound) and under the

104

fttHHHSITTASY GEO LOOT.

tnkmoopt the exact identity of structure of the wood j and
stony portions can be dearly traced. On applying an acid
the earthy natter is removed, and as the ligneous portion
ttxB contains tannin, perfect decomposition had not preceded
petrifaction. The stare of a cask which had probably been
immersed in the well of the castle of Gotha for one hundred
and fifty years, was in part, especially at the junction of the
hoops, petrified by peroxide of iron, sod was so hard as to take
a polish by friction. Where the iroo has been moored by
muriatic arid, the wood continues in a solid and coherent
state. In calcified specimens of the fossil woods of the ancient
world, from various localities and of different ages, including
that from Craigleith, in Scotland, the same results are ob-
servable, the woody fibre remaining after the removal of the
earthy matter by very dilute hydrochloric arid; and from
some specimens, a bituminous oil, emitting a mixed odour of
creosote and petroleum, may be obtained, which is an ad-
ditional proof of the formation of bitumen under aqueous
pressure. M. Gotppert has uot discovered any recent ribbons
petrifaction.

Though wood fossilised by gypsum is very rare, there is a
specimen from Silesia, weighing 4 quintals, in the museum of
the University iff Breslau, of which the ligneous fibre is only
in part fossilised, the rest being flexible. In many ribrious
vegetable fossils, M. GoCppcrt, after removing the silica by
hydrofluoric arid, found the woody fibre so well pr ese r ve d
that it might be used in determining the genus of the plant.
When in fossil woods treated with hydrofluoric acid no organic
matter can be discovered, it has been doubtless re mo ved after
foosiltaation, either by long aqueous action, or by heat.
When slices of the petrified oonifctm of Stksta which still
retain a portion of ligneous fibre are ex p os ed to the action
of a furnace, the fibre is destroyed, aad the i pc d aian s, before
variously coloured, become uniformly white aad opaque, the
characteristic structure of the coutfone bring very distinct. U
Is however, remarkable that the ligneous fibre has been

iUDlMEKTARY GEOLOGY. JQ5

preserved in eome fossil woods found in ligneous rocks, ts
porphyry, basaltic tufa, and even basalt, which must have
been subjected to heat, and it appears therefore certain that
water it a principal agent in the removal of organic matter,
aa M. GoSppert has proved by specimens of fossil wood from
Gists, which had been rolled about in a brook running from
the mountain and contained less organic matter in profiortion
as they were more rounded, or had been more subjected to
the action of air and water, the diminution taking place from
the centre outwards. As in this instance the disorganisation
was effected in a very short time, is it not surprising that any
traces of organic matter should be found in specimens which
have been exposed to the air for more than 1000 years f The
agntixed woods of Hungary, which occur in the horuoutal
bed* of a conglomerate of pumice which forms the basis of
a trachytic group, are externally beautifully transparent, from
the absence of organic matter, and from the presence of water
in the outer portion. Exposed to the flame of the blow-pipe,
tliey lose their traiwj*miry, become white and opaque, and,
from the dilatation of the water, split along the direction of the
ligneous fibre, so that it is possible to sejmratc the ligneous
cells from each other. In the Tokay fossil wood, the colour, as
well as the organic matter, is still preserved ; and in the
Antigua agatised palms, the delicate spiral vessels can still
be recognised. In general, when much organic matter is left,
the specimen is more highly coloured ; but at times the tbit
is derived from the mineral matter. The organic fibre of
fossil plants which remains upon the removal of the stony
matter by aa add when subjected to great heat, is burnt
away, and leaves, aa in recent plants, a sUkioui skeleton ; and
when we reflect on all these carious facta, wa learn with
admiration that not merely the forma of bodies, hot the
organic matter itself of ancient creations has been pres e r v ed
for nor contemplation and study.

The various etrcnmeUaees and conditions of feaeQ vegetables
at all epoc hs have led M* Gotppert to ooocbde that the ferae

106

mtJDIMZKTAJLY GEOLOGY.

which are now in action were sufficient to produce the effects
observed, and that the water of the ancient world did not
possess a higher solvent power than that of the present.
Water dissolves about T *Vvth part of silica, and the ease with
which it entered, as a fossilizing agent, into the vegetable
structure is proved by the concretions on the bamboo, called
tabashecr, and the large quantity of silica deposited iu the
tissues of some other living vegetables.

Coal and lignite are vegetable fossils, and M. Wiegmann has
made experiment* in the moist way to illustrate the formation
both of turf and of lignite; and examples might be cited of cor-
responding cliange* taking place in a natural way, as in frag-
ment h of aueient carpentry changed into lignite from the mines
of CWlnttcnbrmm, and in specimens of w<x>d-work sent to
M. Gotfppert from the iron mines of Zurrach in Stiria, which,
in the space of less than sixty years, had been changed into
resinous lignite ; and in others from the sepulchres of the ab-
origines of Bohemia. According to M . Liebig, hydrogen escapes
in disintegration; whilst in putrefaction, oxygen is disengaged:
when, therefore, the latter change takes place under a high pres-
sure, and at au elevated temperature, considerable quantities of
carbonic acid will be disengaged, and at the same time much
carlxm lx* dcj>o*ited in combination with a part of the hydrogen
of the organic substance, and it is probable that coal and some
lignites have lefti the result of sueh operations. M. Link has
endeavoured to show, by comparative microscopic observations,
that tuff and coal are analogous in structure, and may have
been produced the one from the other ; and stems of trees which
occur in coal are very analogous to those which are frequently
found in successive layers in the deep turf of Ireland. The
formation of coal by immersion in water, under pressure, was
suggested long since by Dr. M*€uUoch. Messrs. Marcel da
Scrrn and L. Figuier have illustrated the general principles of
petrifaction, by the petrifaction of shells in the Mediterranean*
They suppose, however, that the water* of the ancient ocean
Ad poteen a higher solvent power than they do at praam ;

mUDIMEKTARY GEOLOGY.

107

but in reality this difference is apparent rather than real, as
the pretence of so much alkaline matter since deposited in
combination with silicic and other acids must hare rendered
the water a more powerful solrent than it now is. The action
of every natural force tends to a resulting equilibrium,
and if that has now been attained, the same processes will
continue jrithout producing any difference in the great aggre-
gate of the animal, vegetable, and mineral kingdoms ; but if
not, such a difference must, however gradually, lie produced.
The long existence of the present assemblage of created beings,
and the effective condition of the atmosphere, which remains
unaltered by vital agencies, are strong reasons for believing
that an equilibrium has been attained ; and as a further proof,
it should be stated that the world has only lost, during 6000
years, about twelve vertebrate animals, and that principally
from the action of man, although the distribution of animals
has been materially modified by the local extinction of some,
and the lateral extension of other sjiceir*.

fossils amt frt rtf actions. — From the preceding pages the
student must have already learnt that the terms • Fossil' and
• Petrifaction* cannot lie used indiscriminately or considered
synonymous. The word fossil, as understood by Geologists,
means indeed the remains of some organic body found in a
position and under nrcumstanm which prove that it never
could have been a member of the existing system of living
organisms; but it is not necessary that every fossil should have
become a petrifaction — that is to say, have been elianged into
stone — -as is proved by the condition of coal, and still more by
that of lignite, which retains, though manifestly an organic
fossil, the ligneous structure ami fibre. Coal has indeed under-
gone a chemical change by the partial re-adjustment of its
elementary constituents, and the consequent development
within its substance of bitumen, but it has made no approach
to the state cf petrifaction. In like manner, the examples
cited have shown that many organic bodies, in all respects
identical with those now bring, may have become petrified

108

BUD1MKKTA&Y GKO LOOT.

during the course of the still pissing system of creation, and
have therefore do chum to be called fossil. In either case
the mere condition of the body is not sufficient to determine
whether it is or is not a fossil ; and much caution, therefore,
is required in using these terms. The passage of an organic
body from the ordinary to a petrified Mate, which is often
improperly called fosailixation, is influenced by many cir-
cumstances, of which the chemical constitution is one and
will be first noted, — though it is necessary to premise with
Messrs. Scrrea and Figuier, that iu order to induce the petri-
faction of organic bodies, in which process the animal matter
is replaced by mineral substances, they must be plunged either
in a considerable quantity of water which cou tains in solution
a sufficient pro|K>rtion of sihcious, calcareous, or other salts, or
iu semi-liquid muds or other deposits which permit s free
access of such saline solutions : a condition which was fulfilled
in the ancient world when the waters spread over large spaces
now occupied by land which, both from its mineral and
organic characteristics, must hsve been deposited under water,
and when they were rich in dissolved salts, as is manifest from
the extensive deposits of carbonate of lime, of gypsum, and of
rock salt.

The 6me$ and iettk of MmmummU are closely connected with
the mineral kingdom in their natural condition ; — hones con-
taining 561 parts iu a hundred of phosphate of lime with a
little phosphate of m ag nes ia and fluohde of calcium, 12| parts
of carbonate of lime with a small quantity of soda* and chloride
of sodium, or nearly 68 parts of mineral matter combined
with about 32 parts of organic matter ; and teeth containing
sometimes from 64 to 66 per cent, of phosphate of bine, in
the gelatine increases to so large a proportion that
there are only 1 or 2 per cent, of mineral matter, and it will,
therefore, he eanly understood bow rapidly they most decay
and post away, and how little they could be expected to retain
their form and admit of a petrifying change. The lush of
i and the dome of deer are very analogous to taeth and

RUDIMENTARY GEOLOGY.

109

The composition of birds’ bones is nearly (be same as
tbit of quadrupeds, but u they are porous, their density is
much less, and the quantity of earthy matter is therefore less
for the same bu Ik. The bant* of jUktt contain much lest
earthy matter, and on that account are rarely found in a fossil
state. The horns of ruminants, as oxeu, sheep, &c., the scales
of reptiles, and tortoise-shell, are eery analogous, beiug modifi-
cations of the skin, and are poor in mineral matter. Scales of
fishes, on the contrary, contain from 42 to 46 per cent, of
phosphate of lime, and hence are frequently found fossil, whilst
those of reptiles are comparatively rare. M. D‘Orbigwy ob-
serves, that whilst the fossil scales of reptiles are either petri-
fied by silica or carbonate of lime, those of fishes retain a
considerable quantity of phosphate of time, as proved by the
analyses of M. Hnyard; and lienee suggests chemical examina-
tion as a test when there remaius a doubt to which class the
scales should be referred. I' laws, spines, bristles, hairs, and
feathers, are merely appendages to the skin, and, containing
very little mineral matter, putrefy ami decompose so easily as
rarely, if ever, to be found fossil. The shells or crusts of that
portion of the Annelidas called Crustacea, of which lobaters and
crabs are familiar types, contain from bO to more than 60 per
cent, of mineral salts united with various organic substances,
and were, therefore, sufficiently stable to be preserved in a fossil
state.

But, without dwelling on other organic bodice which have
been rarely, and then from accidental circumstances only, dis-
covered in a fossa! stale, let its pass to those which, from their
composition alone, might be classed with minerals, — namely,
the shells of Afettascw. Of all animals, they have left the
greatest variety and number of fossil relics, — a foe i which their
chemiosJ co mp os i tion would of itself explain, even were it not
in part a result of the peculiar conditions and circumstances
under which they lived. The shells of Molluscs consist of
ahont 96 per cent, of carbonate of lime. If of phosphate of
Inns, If of water, and of animal matter only 1 per cant* j or

110

KCDIMSKTAftT GEOLOGY .

in tome thefts, such t» those of oysters, scarcely «n tpprecithle
quantity, which accounts for the great msstet of oyster-shells
(including the allied genera exogyra and gryphaea) which are
found in to many formations. The stony cases of Polyp*, or
corals, are in like manner mineral bodies, as they contain from
97 to per cept. of carbonate of time, besides small quantities
of magnesia, alumina, iron, and silica, combined with phos-
phoric and fluoric acids ; and such a composition explains the
formation of those extensive beds at many geological epochs
which are almost entirely made up of corals, and are so analogous
to the coral reefs and islands of our present tropical seas.

Fossil shells, like fossil plants, occur under various forms :
in some the interior has been tilled, after the death and decay
of the animals which inhabited them, with foreign mineral
matter cither analogous to that of the shells or at times
not so, and a cast has Iwen thus formed in which may be
frequently observed in relief the muscular impressions which
the animal had made on the internal surface of its shell : in
others, a mould has been formed round the shell, and in this
tnanucr the |»eculiar markings, as ribs, furrows, Ac. of the
external surface were preserved, even though the shell itself
had been removed ; and a cast tiring subsequently formed by the
infiltration of sedimentary or disunited matter into the hollow
apace, the external form of the shell was reproduced, though
frequently in a substance totally different from the original car-
bonate of lime ; and again it often happens, that tltoogb the
ahcll appears the same in form and substance as it originally
was, the structure is physically quite different ; and this leads
us briefly to notice the processes of petrifaction, or those pro-
cesses by which an organic body loses more or less of its
primitive nature, and is converted into a new substance, though
•till preserving the organic form.

Petn/meho* by abstract"* of matter . — This is the case
with most comparatively recent fossils, as the boors of caverns,
he., in which the change is almost limited to the removal of
organic matter. It might be supposed that tins limit would

RUDIMENTARY GEOLOGY. )|!

be always observed in fossils of contemporaneous origin with
the shells and other organic bodies still existing, but in the
Mediterranean examples have been discovered of much higher
changes, whilst it has been ascertained that the change is not
perfect even in many older fosails. Thus Messrs. Serres and
Figuier observe, — lstly, that shells art found in the Mediter-
ranean in all stages of the petrifying process, from simple
discoloration to the complete transformation into crystalline
carbonate of lime; 2nd)y, that the molecular structure of
recently petrified shells is very often different from tliat of
ancient fossil shells, the first being usually crystalline, the
others usually compart; though in many ancient fossil shells a
crystalline structure is very perceptible, distinguishing them
at a glance from the surrounding com{>act limestone; and
thus affording another confirmatory argument in favour of the
identity of the process at ail ages of the world. By a com-
parative analysis of the substancr of living, of recently petrified,
and of fossil shells, grnem common to the three epochs of com-
parison being selected, the effects of petrifaction were tested ;
and tt was ascertained that s portion of animal matter was still
existing in shells of the pliocene formation.

The officers of the French Engineers submitted to Messrs.
Serres and Figuier specimens from the neighbourhood of
Algiers, of masses of shells transformed uito s crystalline
white limestone of • peculiar lustre, like that of alabaster. In
these shelly masses, small rolled pebbles are observed in-
crusted by a stalagmitic glair, which appear* to be similar to
the cementing substance which binds Uic pebbles together.
The shell* are all of recent »j»eeic* of the genera pecttmculu*
and cardium, with a few univalves, axul the rock itself is con-
sidered by the officers of Engineers to be decidedly of recent
origin ; and another interesting fact may be cited in the
remarkable conglomerate now forming on the shore of &anU
Maura, and at other localities, and which in its cohesion ii
fully equal to many ancient rock* of the same description ;
there being a continued tendency to such aggregations, even

112

KUDIMIKTAKY GEOLOGY.

from other than calcareous agencies, as is seen in an interesting
specimen, also from Santa Maura, presented to the anther of
this volume by Mr. Cot tun, in which several pebbles have
been agglutinated firmly together by the decomposition of a
nail, to which they stiD strongly adhere ; and in a similar
instance at one of the batteries of Portsmouth, where a con*
glomerate has been formed round the iron shoes of the piles.
Messrs. Serres and Figuier state also, on the authority of others,
that the cardium edule, in a petrified state, forms considerable
beds at the mouth of the Somme, and that at Caneale the shells
of oysters have been petrified in the same manner as in the
Mediterranean.

Petrifaction by tarraWa/io* it a combined mechanical and
chemical process, in which a body becomes enveloped and par-
tially penetrated by mineral matter which is deposited upon it,
just as cry stals of alum or of sugar are formed round a thread
or stick when plunged into a maturated solution. The substances
usually concerned in this operation are carbonate of lime and
silica, more jiarticularlv the firmer, which is soluble in water
containing carbonic arid, as all spring water does. The manner
in which such incrustation is effected may be readily observed
in fountains and springs which are highly charged with car-
bonic arid, as the excess of arid escapes cm coming into contact
with the air, and the calcareous matter incrusts the moss, leaves,
or other bodies exposed to it* action. When this b k»geoo.
tinned, a mass of calcareous tufa b formed ; and in a similar
manner, In fossils, a crust might hate been formed sufficiently
thick to retain the form of the body after its substance had
been removed by decomposition. As the deposition of matter
proceeds, it will fill up the cavity, and thus become a cast of
the organic body : here, therefore, similar results may be ob-
tained as in the preceding cases. Sulphnret of iron and of
copper, peroxide of boo, and some other substances, occa-
sionally occur as intrusting bodies ; and in the tertiary days
concretionary incrustations are freq neatly (bond enveloping
organic bodies, which, though altered, have not been entirety,
replaced by mineral matter.

KDtMIVTAftT OEOLOOT.

US

Petrifaction by tie meciomcal introduction ee dim entorf
wmtter . — Where the organic body pmeoti a large and easily
accessible cavity, mineral matter gradually fills it up. This
matter is sometimes very coarse, and it is in this manner that
petrifactions in sandstones have been principally formed. En-
veloped in and filled with sand which has become cemented
perhaps by matter proceeding from part of its own substance,
the organic body, whether a bone or a shell, may be entirely
destroyed, and thus at once leave a mould of its exterior and a
cast of its interior, or it may be only modified by changes
which will be now described.

Prtrifmctio m by molecular penetration and by substitution . —
When an organic body has been partly disorganised, it may
become to porous as to allow even fine matter held in
suspension, and still more so matter in solution, to penetrate
through it* tissues, or, in other words, solid matter may be
that filtrated through the organic body. In this manner a body
may be permeated by mineral matter long before the total
removal of its organic constituents, tnd whilst the more acces-
sible cavities have been filled by coarse materials introduced
through distinct openings, the iulemnl cavities may be also
either filled with very fine matter which has passed through
their coatings or walls, or lined with crystals separated from
matter in solution. This change is sometimes so complete that
it amounts to a substitution of one form of matter for another,
and the result, therefore, represent* in every minute particular
tbs original body, though in a totally different substance.
Vegetable fossils afford many examples of this substitution of
mineral for organic matter, and it is often possible to detect in
the petrifaction the most delicate vessels of the organic body,
and thus to determine with the greatest precision the genera
of plants. In plants this substitution is principally effected
by the inirodueticuPcf silica, and in like manner the animal or
more purely or gani c portion of other bodies are also petrified
# by sdidoos matter; the ligaments, for example, of gryphites
alkkm whilst the shells are ca lca r eo u s, nod the

114

MV DIM EKTAJtY 610 LOOT.

interior of many echinidse, or aea-urch ins, being filled with
«lex whilst the thin crust or shell remains calcareous, there
being apparently an elective affinity between organic matter
and silex.

Petrifaction by chemical change and by transformation . —
In these cases there is no mechanical introduction of mineral
matter into an organic body, but a chemical action by which
either the original component parts of the body are brought
into new combinations, as in the change of organic structures
into bitumen, or the elements of the body are made to combine
with external substances, and thus to procure a metamorphosis
of the fossil, as regards its composition. In the case of irons-
formation , there is actually no change in the substance, but
merely ait alteration in the molecular arrangement of its par-
ticles. This change of physical condition might be illustrated
by reference to the changes which are effected in sulphur and
phosphorus by beat, and it is abundantly exhibited in fossil
shells, which, though when recent they are comjiact, or rarely
fibrous, become in the fossil state lamellar, crystalline, and
finely fibrous, or undergo other physical changes, such as that
from ojuunty to translucent?, &c. In ancient petrifaction, car-
bonate of lime was the principal agent, and the fussilisation was
comjdete in projection to the abundance of that salt present.
Iu gypseous, argillaceous, and even sandy deposits, petrifaction
is imperfect and the shells of moliusca are only in part pre-
served. 5

Water dissolves carbonate of lime when an excess of carbonic
acid is present, as is always the case in nature , and in conse-
quence, an appreciable quantity of bicarbonate of lime exists in
•ea water, and is one of tlie many examples of a balance between
the formative and destroying causes constantly in action.
Innumerable springs charged with carbonic acid dissolve the
carbonate of lime of ancient formalkmap and carry it to the
ocean, whilst the moliusca, kc. again withdraw it, and liberate
the carbonic add to return to the a tm o spher e. The s hel l s of
the moliusca again pass into new mineral deposits, either whott

KGD1MKNTSJLY GKO LOGY.

115

or triturated into powder; ud the tame may be said of the
malt and other xoophyte*. In regard to silica* which is the
next most important petrifying substance, and even exceeds
carbonate of lime in the extreme delicacy and fidelity of the
restoration it produces, it has already been stated that the
water of almost all mineral and thermal springs cotitaias a
portion of it, that it occurs in most rivers or streams, and that
it abounds in the stems and membranes of many vegetable*.
Combined beat and pressure favour its solutiou, — as is abowu
by the great quantity deposited at the foot of the boiling
Geysers of Iceland, — ami it is gTeatly promoted by the pro*
•race of an alkali which is usually afforded by the decomposi-
tion of rocks ; and further, in the gelatinous or uancent state,
in which it always occurs on the decomposition of s mineral,
it is readily soluble. Silica, therefore, must have been in
solution prior to the formation of rock crystal, and, probably,
in a gelatinous state wheu forming chalcedony, opals, and some
of the Hints and cherts of various geological formations.
Oxide of irou, anhydrous or hydrated, and biaulphurct of iron,
have also entered into the formation of fossils i in rrsjwct to
the latter, the change, as in silica, is principally produced on
the animal substance ; for example, the ammonites in shale
exhibit a mere film of shining iron pyrites, which has replaced
the animal membrane.

From the processes of petrifaction, it is necessary to turn
to the consideration of the mineral beds in which petrifaction
occurs, and to determine the exact relations of the bed* to the
fossils they coutain. On studying the still passing operations
of Nature, it becomes evident that many forms of mineral
deposit are in course of production, such as the sand dune or
hill, which though removed from the action of the sea is still
shifted and modified by the action of winds, and in which land
and marine shells and fragments of bones arc enveloped by the
drifting sand, and the various deposits of mud, sand, gravel*
or shingle, forming in the hays and estuaries, or on the coast of
th* o c e an, in all of which relics of organic bodies may hats

116

ftVDlMBKTAftY GEOLOGY.

htm tttonbcd, as iha same fom which operated hi moving
thi mtftd or gravel vn squally efficient for transporting the
oty nic bodice. Bat in them rases there may not here been
•n origins! connection between the fossils end the mineral
beds in which they are found, the inhabitant of s sandy sea
bottom being homed, when no longer poss e ssed of a vital
fom of resistance, by the currents and deposited amongst
the muddy sediment of an estuary. Many such c o n f used
assemblage s must doubtless have been formed, but the correct
observations of modern Zoologists afford a clue to the discovery
of the real inhabitants of the several deposits, and to the sepa-
ration from them of extraneous bodies ; for example, it baa
been determined by Professor Edward Forbes that the vertical
range of marine molluscs is restricted to definite limits, so that
some are specially littoral or shore inhabitants, and found
on the rocks or on the gravel or sand which is washed and
left dry alternately by the tidal wave, whilst others live at
successive and increasing depths below the surface of the
ocean. And further, it is known that some molluscs or
shell-fish live buried in the sand or mud, whilst others
rest on the bottom, either adhering to stones or rocks, or
kept in their place by their weight alone » so that a careful
comparison of s duster of such fossils will greatly a ssis t the
skilful Geologist in determining which should be assigned to
the particular bed as its natural inhabitants, and which should
be considered extraneous bodies derived from drift, and thus
to recognise the influence exercised by the petrographic con-
stitution of the bed itself on its fossils. Organic beings are,
indeed, not only restrained to a particular medium in which
they can alone live, hut require also s peculiar collocation of
circumstances suited to their individual existence: thus one
fish may he marine, another fresh- water, — one may live in open
and deep sens, another frequent rocky coasts and dear water,
a third ddight in the muddy shallows of estuaries; and in
a similar manner mollusca an regulated in their habitats by
the necessary requ irem ent! of their organisation j — a kmpit

KVDIMimRT GEOLOGY* 117

being attached to a rock, and able to sustain the heeling
action of the ware, — the cockle inhabiting the gently-eloping
sandy shore in shallow bays, — the myacea burying themselves
in wrni l ar strands, — the pinme frequenting the muddy bottoms
of deeper waters, — whilst many genera with strong shells can
beer the force of currents, and rest uninjured on shingle banka
or rocky bottoms. As the Naturalist, therefore, does not look
for the animal suited to a muddy bottom on a shingle bank, or
for the thin-shelled spatangus at the bottom of a rocky diff
exposed to the violent action of the tidal current, so the
Geologist mnst exercise s like caution in hit r e sea rch , and
remember that — 1st, A peculiar petrographic constitution in a
stratum will be secoinfuuiied by a peculiar paleontological
assemblage of fossils ; and 2ndly, That suck s paUeontologtoal
assemblage does not naturally include genera and species
suited to strata of a different petrographic constitution : and
therefore, when genera or species peculiar to one form of
mineral stratum be found in another, they may be expected to
he rare, much less develop!, and less distinctly characterised
than in the stratum to which they properly belong.

Combining the artual mineral structure of the stratum,
which is a result of certain necessary conditions, with the
modifying circumstances of position, deposits may be con-
sidered as shore or littoral deposits, shallow-sea deposits,
deep-sea deposits, coral- hank deposits, Ac. ; ami the probable
occurrence of organic bodies must depend on their adaptation
to those eimimsUnees. so that it may he assumed, aa a eery
important character, that in organisms of the coralline type of
deposit, the shell or crust is massive, and marked by ribs,
stria?, spines, knobs, and other peculiarities, which, whilst
they doubtless sddrd to their fitness for opposing the contin-
gencies of their peculiar location, now afford so many valuable
characters for studying them as inhabitants of aa ocean long
since passed away. Shingle deposits produced by the more
active wear of the waves, though often intimately co nn ected
with coral hanks, accompany and link together a& the petm*

118

BUfHMCKTAmY 6 VO LOOT.

graphic forms of deposit. They possets few zoological pecu-
liarities, borrowing, as it were, the characters of the several
deposits with which they are connected, by receiving from
them the fragments of their various organisms, which are
gradually, as they are carried along, worn down, passing
through an oolitic state into an impalpable paste. Muddy
deposits, such as marls, compact and sub-compact limestones,
together with sands and sandstones, constitute another im-
portant class, and exhibit a totally different zoological assem-
blage : the corals are of spongy and intrusting genera, and
generally without apparent base ; crinoids are rare, scattered
about, and generally of unattached genera ; the echinida are
leas rare, particularly the true echini and their congeners, and
the spatangi abound in muddy and sub-sandy deposit*. Of
the attends, the genera interim and ophiocoma are character-
istic of muddy deposits, and of tine sands and gravel. Of the
acephalous mollusca, the genera which abound an , solen,
pholadomya, myopsia, pinna, tollina, mytilus, modiolus, cor-
buta, taocardium. cucullca, and amongst the ostrarea, gryphwa
and exogvrm. In the gasteropoda may he noted, rostellaria,
pteroeerm, nation, turrit oils, fasciolaria ; and amongst the
cephalopoda, the genera nautilus, ammonites, belrmnites,
being either rare or abundant, according to the variations
in the form of the deposit. Fish with pavement-like teeth
are very characteristic of these mud deposits ; and reptiles
are especially abundant in the Jnraaic beds, though they are
locally rather than generally distributed, o cc u r ri ng in what
a nay he deemed muddy shore deposits. A general and con-
stant character of all zoological assemblages in muddy deposits,
is that the prevailing genera and species are provided with
shells or cove rin gs not fitted to withstand the wear of trans-
port, being smooth and thin ; and in those genera which
p o sse ss s thick shell, the tissue is nearly noadntk sad
easily disintegrates. It may be also stated, ns distinctive
of muddy bottoms, that the genera are mom frequently
free than attached, even the stems of pe n tac rini not cdbibtfr*

KVOIMKITTAET GEOLOGY 119

tag strong root*, haring been probably tied by fibrin** or
simply immersed at their basr in the mud.

The sab- pelagic and pelagic forms of muddy deposits,
though c o rre spon ding to the littoral form in their petro-
graphic conditions, are diftinguiahed from it by aoofogical
peculiarities.

The deep-sea or pelagic deposit* are eery uniformly con-
stituted. homogeneous, regularly stratified in continuous and
often massive beds, except where modified or disturbed by the
action either of currents or of elevating forces. In these
deposits, large spares are often deficient in organic bodies, or
contain only their debris, together with those spongy and
fibrous rortU winch are supposed to inhabit the waters of
great depths ; and where <vph*lo|>oda abound, the species
differ from those which inhabit muddy shore dqiosits.
M. (iressly arrived at these important deductions from the
prmwl»M« facts, haring thus as it were adopted views very
stniilsr to th^w which have been so ably set forth by Pro-
fessor Fori***

1 Karh class or form of deposit presents characters, petro-
graphic, geognostic, and zoological, j»ectiliar to itself, and dis-
tinct from those of any other class or form of deposit, although
of the same geological epoch.

2. That the same class or form of deposit, as regards ita
petrographic and geognostie condition, exhibits very analogous
zoological characters in each successive geological formation in
which it occurs. These two laws are of great interest, and
highly important in the application of soological characters to
the determining of geological formations ; though it is neces-
sary to take into account, as already pointed out, every disturb-
ing or modifying influence, in order to separate, in any
attains), those organisms which are peculiar to and must ban
found a fitting habitus in it, from those which have only been
brought into it from other situations by currents, storms, kt.
In the muddy sob-pelagic bottom of the channel of Corfb, in
the Ionian islands* many of the thin -crusted and sSfty-apbad

ISO

IVDIMSKTm CEO LOOT.

apatangidm ire found, together with roeubr, tellmm, corbula,
and other organisms fitted for such a habitus ; but these are
combined with abundant exon* of other organisms foreign
to such a habitus, — as the ralres of strongly-ribbed cardie,
pectins, Ac. In the one case, the shells, Ac. are generally
perfect or alire ; in the other, more frequently separated and
injured ; and in bir sires though still connected, they are often
found open and the rakes twisted round ; and the Geologist
will find many similar cases in the deposits of ancient worlds.

3 . In erery petrographic class of deposits, two sets of
organisms may be expected to occur : the one suited to the
habitus afforded by it* geognostic position, and therefore the
truly characteristic organisms of that class of deposit, or those
which should be used in any comparisons between distant
deposits of the same or of any other formation ; the other, ex-
traneous organisms, the absence of which at tome other
locality would not be rridence of a geological difference, but
simply of freedom from the modifying influences which hsd
affected the first locality. There are many other geological
facts on which much light is thrown, if they are not fully
explained, by the method of comparing the conditions of 100-
logtcal existence at ancient efiorlui with those of the present,
such ss the abrupt terminations of peculiar petrographic
deposit!, the local distribution of fossils, Ac., cases which can
be observ'd wherever a mud or other bank is cut off by a cur-
rent, or where a local deposit is formed under the lea of pro-
jecting rocks, or the shelter of a coral reef ; hot it would be
vain to attempt to note them all, and enough has been said to
guide tbe observer to a right mods of geological inquiry in
tracing out tbe lateral extension of any particular formation.
When the inquiry is made in a vertical direction, or by the aid
of natural and artificial sections, the obeerver will find the
hum cla ss e s of deposit recurring at different intervals, and
will discover a rimilar analogy in the >s»emhlsgf of organisms
connected with them ; an analogy, such as riasiiar conditions
of Hriatmoo must produce,— not an identity, which could

*xnmisirr*xY osoloov. 191

tiara identity » the at frahrat of the two periods.

He is thu# led Is another geological rale or principle.

4. Similar variations in the o oo dit i o n a of orgeats esiatencc
mast produce nastier modiflcotiooa in the eeeemliiegi of organic
beings which exist in nriovi pieces et the seate epoch. Went
of identity, tboefoct, ie the organisms of the seme p e t rographic
dees of deposit in sneer t e i f e portions of s section of ear pert
of the earth’s crust, cannot be explained by e variation of the
conditions of existence ; the petrographic and geognislic ictot*
Uif combine with 0* soolugical mamlapy to show that the
conditions were really the same, and the change must he
ascribed to a difference in the aggregate fauna and flora of
the epoch : or, its other words, it proves that the organisms of
successive strata were connected with distinct acts of creation,
or formed parts of distinct organic systems or worlds.

As a relation exists between the shell or covering of tlss
animal and the petrographic condition of the deposit iu
which it is found, it must be assumed that the animal
itself was fonnetl to exist under the }»hysieai forces which
gave rise to that deposit, and that its general organisation
was suited to all the circumstance# of its destined habitat.
Temperature and pressure are the two forces which most ma-
terially affect marine organic existence, and restrain or promote
the distribution of marine organic bodies ; hut it may be asked
in what manner the stream of organic life commenced ) The
earliest historical record of the human race describes a local
creation ; and though the learned dispute os to the precise
time involved in the events noted, the Mosaic account b in
favour of the theory of a centra of creation : and if the past
worlds of former geological epochs he also taken into con si d er -
atioo, the more general principle of centres of creation may ha
safely adopted os more conformable to the simplicity of Qiturt,
than a contemporaneous or even a successive creation of ths

A group of animals being cruet id with orgamrutious raked
to certain conditions, such ns the breathing of air nr water, god
9

123

lvotMurritr obology.

the capability of supporting a certain degree of beat or amount
of pressure, when the mandate was proooonord that they should
multiply, their lateral p ro g reaaio n on the earth would be con-
trolled by the laws implied by those conditions. In this way
the course of the marine molluscs might be traced laterally
along the ooaat at the depth suited to their structure and habits.
But life is not the only active force ; the tidal ware and the
great marine currents are in motion ; the sea beats against
the shore, and the detrital matter of the rocks is carried for-
ward and deposited in new strata, by which the shallow water
is made dry land, the deep water shallow, and the advancing
mollusc is thus impelled, by the necessity of keeping at a
definite depth, to pais from the surface of one bed to that of
another i and if the general conditions remained the same,
species may have thus lived over s space of time during which
a long aeries of deposits were formed, and in consequence
their fossil relics might be found through an extensive range
of strata. This combined lateral and vertical extension requires
time, and it may be therefore assumed, as demonstrated by
Professor Forbes, that fossils which have the greatest vertical
range, or bare existed for the longest time, have also had the
greatest extension in space.

Heat is the other great regulating cause which confines the
progre a aion of land animals to narrow iixxiita. If fitted to a
temperate climate, they must as they advance southward seek
it oo higher ground , and as the mountains of the earth are
comparatively small, the range is limited and the extension
soon stopped. In marine animals the case is varied, as will
be understood by referring to the conditions of temperature in
the ocean. It has been stated that the temperature of the
earth increases in proportion to the depth below its surface :
in the tea it is the reverse, as the temperature decrease* with
the depth, even at the tropica, until it has armed at a very
little above 32*. This to many will appear a contradiction,
but it ia not eo * the outer crust of the earth is cooled on dry
hud by radiation or by radiation and transmisaion on had

mtn»ti«t*TA*Y OMKxnr. ID

e om fd by sea ; but the pas s age o f but b dnr through (hi
earthy vtteriik of the upper crust, whilst H k rapid through
the aqueous c ov e ring $ and it is therefore quits accordant with
the kws of nature that She earth at the bottom of a sea many
mike deep should be icy cold, whilst at a similar depth in the
solid matter of the earth the heat would be sufficient to melt
iron. Eero in the tropics, as the sun's rays set but feebly
on the water, and can have eery little beating effect on the
ground at great depths, the temperature would not eiceed the
mean temperature of the place, rren if no interchange of water
took place, except from below upwards, and met wratf .* but
this is not the case, as water of a mean lower temperature will
gradually more from north to south, until a general mean
temperature has been attained by the ocean except in that
merely superficial portion which is subject to the local in-
fluences of heated land, a portion which is deeper as it is
nearer to the tropical or more heated regions. The eery care-
ful experiments of M. Ch. Martins in the corset t* La Uttktrtk*
are perhaps the most interesting on record. They were made
in the Polar Seas, in the months of July and August of the
years 1 838-9, and extended to the depth of 870 mitres (2781
feel), giving a uniform decrease of l J° Fab. for 320 feet, or
*69 cent, for 100 mitres, the final temperature arrived at being
very nearly 32°. Parry and James Ross found the tempera-
ture lower, as it was only 28|° si the depth of 2304 feet in
July, 1827. The equalisation of temperature is further
assisted by the flow of the heated equatorial waters towards
the Pole, as is seen in the Gulf Stream, which, notwithstand-
ing the doubts entertained by some on the subject, is traceable,
according to II. Martins, to the North Cape, This uniformly
low temperature of the depths of tbs ocean materially restrains
the dispersion of tnimak suited to a high, and favours that of
suited to a low tempe rature ; and therefore ex plains
many of those snomkirt which occur in the habitats both of
rece nt and foasR specks. But the bottom of tbs ocean k not
> of fresh mineral matter | it k sub-

134

tOOlllflltAtY GEOLOGY.

jeot to «& the tocttpcei of elevating forces, and it h tbers
fon highly probable that the propwaon of animal life is
•topped at one point by an elevation of the bottom which brings
it within the influence of a temperature destructive of the organ-
isms then living upon it, and at another promoted by a depression
Of the bottom, or vice vcr&d ; and in tliis way various modifies-
tions of the groups of organic beings, and many abrupt termi-
nations of them, must have been effected at all periods of the
earth’s history. These principles serve as a guide in investi-
gating the topography of the ancient world ; and, as pressure,
independent of temperature, ads as a limiting force, it cannot
he supposed that even the molluscs could be distributed with-
out the aid of hanks or shoals to preserve a suitable depth ;
or that the mammalia could have spread over the earth without
a continuity of land, as air is essential to the presen ation of
their life. The development of the earlier fosailiferous strata
implies therefore a continuity of the ancient should of those
epochs, and it hence appears that Australia was, to a certain
extent, connected with Europe at the epoch of the carboniferous
deposits ; or, ascending to newer dc|>osits, analogies between the
past and present creations are found in the oolites of Europe
in the relics of marsupial animals, in the remains of fishes ana-
logous to the Port Jackson cestracion, and in the remarkable
genus trigouia, which still exist* in Australis. This recurrence
in Australia of a toologtcal type characteristic of the Oolitic
period raiders it probable that Australia and Europe were
then connected by dry land, as in the carboniferous period
they were by shoals ; or may it not he possible that tome
of the molluaca and plants of Uie carboniferous epoch, which
are associated with oolitic plants in the Australian coal field,
arrived there by combined lateral and vertical extension at a
geological epoch posterior to that of the coal formation of
Europe? In the tertiary periods, or thorn immediately ante-
cedent to the present, many exam pies may he traced of con-
tinuity of land wow wo longer existing; apd Geology and
PafaNBtokgj b ec o m e guides to inte rpret the grant

in

which bam take* pkt» at wme e nm n epoch*, and to npmw,
Mknn,iW whom phoooo of tin glob* oaudot all it» chofto t
rl tiring mj (boat cloudi of uaccrtaiotjr aod that aa fta ha
which had before hafled the atadaat of nature) cad interfered
with hie perception of truth.

CI1 AFTER VI.

General sad Practical U*m*rk* oa Geological Formations.

In studying « geological formation, by which term ii under-
stood a reprracntatioo of the mineral and organic conditions of
the e«rth at some former epoch, the observer will meet with
eridenors of each description of formative process, the natural
history of the earth implying an investigation of the changes
both mineral and organic of each attccetatve epoch. To
express the relation between eruptive, metamorphic, and sedi-
mentary rocks, a eomj»otind nomenclature, representing at
once the epoch of original deposition and that of meta-
morphism, 4c., baa been projioard by Sir C. Lyell, as Ante-
Cambrian carboniferous metamorphic strata, triasic oolitic
metamorphic strata, 4c , by which is meant that the strata
were respectively deposited prior to the Cambrian, and during
the triasic, but reduced to their metamorphic condition by
force* acting during the carboniferous epoch in the drat
place, and the oolitic in the second ; and in like manner
there may be Ante- Cam bnan platonic, Silurian phttonic,
carboniferous platonic, truunc, oolitic, err tacrotts p Niton ir,
4c. i or Silurian volcanic, carboniferous volcanic, triasic,
4c., up to the volcanic rocks still forming*, and though it
t» difficult in very many cases to determine with certainty
the actual epoch of the original condition, or of the mournor*
pbic change, of the crystalline schists, and also of the
upheaving and apparent partial eruptions of the platonic rocks,
or cron of the eruptions of volcanic rocks, it most he admitted
that the proposed nomenclature ie correct hi principle.

; 26 KvitxtirrAftT okoloot.

From • carefol comparative study of the zoology and phy*
tology of stMcmive epochs of the earth’s history, as displayed
by organic relics formed in the mineral deposits. Geologists
have established a certain number of distinct formations, cadi
of which is characterised by its own animals and plants, and
which are exhibited in s descending order in the accompanying
Table.

According therefore to Cotta, the total thickness of stratified
fittsiKfrvoos deposits is 22,750 feet, or shoot 4} nuke, exdn-
siv* of the variable and ascertain deposits of the existing

KVMlttKTAftf 0*0 LOOT. \tj

period ; but each estimates art only my rough approxima-
tioM» at the thick one of each deposit may be expected to my
in ettry locality, and to undergo very material modi fi c a tion s
both b the character and proportions of it* several parts*

In the remarks on these formations, the ascending order
wtQ be followed, the lowest recognised strata being first
noticed, and each successive formation, growing as it were
one out of the other, will be considered in the order of its
o cc ur rence.

CAMiaUff, TftK KsaUKST KNOWN FOSSIL DKFOS1T.

This term has been applied by Professor Sedgwick to stra-
tified rocks which occur in Cumberland, North Wales, and
other places, under the decidedly Silurian strata, and are for
the most part slaty and without fossils. They contain but a
small proportion of time, and their fossils bring local and rare,
sufficient evidence has not been obtained for placing them
in a toologica! order distinct from that of the Silurian. The
apparent thickness of the slaty and gritty beds is considerable,
but this is due to contortions, by ahich the same beds are made
to appear srrrrml timet successively in the same section. Hie
prevalence of the slaty cliaracter shows that the progress of
formation ha* not been varied by much original disturbance,
and the thickness of its beds indicates the probability of some
portion haring beet) a deep-sea, or rather semi-pelagic deposit.
The Cambrian is now considered a marked group b the
Silurian, and as the Cambrian group placed at tba base of
that system.

•ILUaiAN.

This formation, since the publication of the splendid work of
Murchison, has attracted the attention of all Geologists;
and as it exhibits the rcbes of organic beings in great abund-
ance, and of very peculiar forms, has been rescued from the
formerly obscure tegions of the grauwseke, and reduced to
light mid order by the discoveries and research of Sir R.

KVMXtVTAIT 0X0 LOOT.

120

Murchtsoo and kb follower*. The lower group of thb Older
includes the Llandeilo flags, or micaceous slaty grits, and
shore them the Caradoc — ndstooc. The next in order ascend-
mg b the Wdod group, cons istin g of a deep bed of shale,
surmounted by a bed of limestone ; and the third or upper,
the Ludlow, co m p risi ng the lower Ludlow shale, the Aymeatry
limestone, and the upper Ludlow, a calcareous grit or sand-
stone. In England these groups follow each other in actual
sequence of superposition, and are distinct in order of time;
hut in other regions the sequence may be varied in conformity
to the laws of geological deposit : whilst, therefore, in Nor-
way and Sweden there is a partial similarity m lithological
character, and the conditions of deposit hare been nearly the
same, limestone has been much more developed in many parts
of North America, and the conditions of deposit hare been
different.

in the combined Cambrian and Silurian formation the earth
first exhibits traces of life, and we find the remains of fishes
strange in form, but high in orgsnixstiou, such as the genera
onehus and plectrodus, many molluscs, including peculiar forms
of the hrachiopods and cephalopoda ; very characteristic Crus-
tacea, belonging to the extensive family of triiobitem, which,
beginning to exist at thb early epoch, flourished in number
both of species and individuals, and then rapidly passed away,
the family being traced no further than the carboniferous order;
radiata, tare ; aoophyta, leas abundant than in succeeding
order*, bat exhibiting some peculiar forms. In respect to the
conditions of deposit, it may be observed, that though the ex-
tensive limestone strata of thb epoch, adjacent to the great
lake* of America, were probably pelagic (the large orthocene
and many braobiopoda having been well suited hr deep aeas),
and formed, kkr the mountain limestone of the carboniferous
system, and even like some deposits of the recent epoc h , by an
accumulation of the remains of testaoee, or, on the temporary
ccsmlioT) of the influx of mud, by the growth of corab suited to
aoeb tht trideooe afforded by the hmdd of Engimid

MU Dim NT A KT GKOLOOY.

m

md Ireland, particularly by the trilohites, the many spades of
ttocula, ami nren it may be added by the fishes which were
probably fitted to grovel in the mud, indicates local deposit* of
mod and sand in moderate and aometimea shallow depths.

The in vertebrate fossils which have not hitherto been dis-
covered in any more recent deposit, excepting in some instances
in the Devonian, are graptolitea, which are soophytea related
to the pcnnatula ; chain coral, catenipora encharuidrs ; many
geocra of trilobites, such as remopleurides, phacofut, ralymene,
aaaphus, ampyx, triuucleus, harfies, b routes, and several others j
of brachiopoda, the gruus |>entammis ; of cephalopoda, the
genera phragmoerrss and lituite*. &c., the great development
of the nautiloid type of molluscs living a remarkable fact in
this early jKirtmti of the earth’s history ; but it is impossible
to notice here all the peculiarities of the many remarkable
fossils of this formation without entering largely into their
natural history ; nor is it necessary to state what fossils cha-
racterise the MibditUiou* or group* of the formation, as it is
enough, in a practical jwnnt of view, to lie able to rctx»gmx«
the existence of the formation itself ; which is of much
importance, as it lies below the great carboniferous system on
the one hand, ami on the other overlies a scries of metamorphie
rocks, embracing the useful deposit* of various descriptions of
slate and other building stone*.

In die classification of M. D'Orbigny tlie Silurian system is
divided thus : —

. / B. Miirrhisoniati. or upper.

(uturwn | ^ HllunMOt „ hwtr . U

Mod he enumerates 33b specie* of mollusca and fit of nuliata in
the upper, ami 37 3 spec ic* of mollusca and .VJ of radiata in
the lower dmunm.

Many of the schistose beds yield good (lags and slates.

Besides the various localities of Europe and America, the
formation has been noticed at the Falkland Islands, and in
South America. In Husain and in North America this forma*
taou is frequently exhibited in the actual state of its original
W&

130

BODIMENTABY GEOLOGY.

deposttkyn, occurring in widely - extended horizontal beds
abounding in fossils.

DEVONIAN, OB OLD BED SANDSTONE.

This order, so long known under the name old red sandstone
— a term nearly as obscure as that of granwacke — has, by
the researches of Professor Sedgwick, Sir R. J. Murchison,
Sir H. Dc la Bechc, and Messrs. Phillips and Lonsdale, been
raised to the rank of a distinct fossilifcrous formation. Viewed
as sandstone and conglomerate in the light of drift, it appeared
difficult to connect it with the limestones of Devonshire; but
when similar limestones were fouifd ou the Continent in similar
positions, the limestone of the Eifcl being thus placed, this
difficulty was rrmoved, and the formation was found to embrace
the usual assemblage of argillaceous, sandy, and calcareous
strata. In Scotland, end on the borders of Wales, it occurs in
the form of a red sandstone and conglomerate, associated with
shale and marl ; the conglomerate and sandstone at the top, the
variegated marls and impure concretionary limestone (corn-
stone) in the centre, and variegated micaceous or quartxoae
sandstone splitting into tiles (tilrstone) below. In the North
of Scotland many peculiar forms of fishes have hern found in
the lower division, whilst in the upper, comprising the belt of
yellow sandstone, appears the genus boloptychus, which extends
into the carboniferous order. Were this portion alone of the
system studied, it would appear to be connected with the carboni-
ferous rather than with the Silurian, and it is so placed by
Cotta ; but when the Devonshire and Cornwall strata are ex-
amined, and compared with those dT the Eifel, the presence of
species common to the Devonian and Silurian on the one hand,
and to the Devonian and carboniferous on the other, impress
upon them a different character. In consequence of this mixed
distribution of fo ods, Professor Phillips has proposed to
embrace under the general term palsposoic, the Cambrian and
8«htriaB m the lower palaaoaoic, the Devonian at the middle

sal tbs carboniferous as tbs upper pslansoic, to

UUDIMENTA A Y GEOLOGY.

131

which Sir R. MurchUon has added the permian, including the
magnesian limestone. Of 2/5 species in the Devonian strata
of Devon and Cornwall, Professor Phillips states that 25 have
been found in the lower division in Englaud, 5 1 in the upper
division in England, and 57 in the Eifcl and Bcnsbcrg,

The very dilapidated condition of many of the fossils of this
formation shows that they have been drifted into the deposit;
the trilobites and many other fossils of the Silurian epoch
described by Professor Phillips being generally in a shattered
state : if then these fossils, and many of the zoophytes, Ac.,
were brought in by drift, it is very possible that they were
living elsewhere at the time of the deposition of the Devonian
strata, and that the actual zoological relations between the
Silurian and the lower Devonian are closer than would be
inferred from such fragments alone. Professor Phillips
seem* to adopt this opinion, that there is a considerable
analogy between the lower Devonian and the Silurian on
the one hand, and on the other between the upper Devo-
nian and the carlwniferous. Cotta classes the Eifcl beds
with the Silurian ; but if Silurian, they occupy a higher posi-
tion in the series than any of our English or Irish beds, and
must therefore 1** parallel, as shown by our English authors,
with the lower Devonian. M. D’Orbignr states the number
of mollusca at 1054, and of radiata at 146, — numbers so great
when compared to the more derided formations below and
above, as to strengthen the belief that many of them arc
extraneous.

In referring to the use of fossil evidence it should therefore
he remembered, that as any fossil species of an early epoch may
he continued upwards, or drifted into more recent formations,
the appearance of a small number of such fossils cannot be con-
sidered sufficient evidence to place the strata containing them
in the older formation, unless supported by the general group-
ing and arrangement, under the same petrographic characters j
whilst on the contrary, the appearance, in any bed, of faints
characteristic of a more reoent formation, must always be

132

KUDIMKKTARY GEOLOGY.

strong presumptive evidence against its antiquity. Dr. Man*
tell and Capt. Brickenden have announced the discovery in
the Elgin sandstone (considered a portion of this system) of a
new reptile, in which the characters of lixards and frogs are
blended together, and Dr. Mantel! has named it Telerpetan
Elffineme. Professor Forbes has also announced the discovery
of fresh-water shells and plants in the old red sandstone of
Knock topher, county Kilkenny, Ireland ; and these two facts
of the existence of air-breathing reptiles and of fresh-water
animals and plants at so remote an epoch, are singularly con-
firmatory of the analogies between the past and present states
of the world.

Practically, many beds of this formation, especially of the
yellow sandstone, are excellent building stones ; whilst the
decomposition of its marly beds produces a rich productive
soil. The limestones sre valuable both for building stone and
lime. In Russia, south of Petersburg, a large area, formerly
supposed to belong to the new red sandstone, is of this geolo-
gical age, though abounding in saliferous and gypseous beds; —
being another proof that salt deposits liave, in very similar
circumstances, been formed at various geological epoch*. The
determination of this formation is important, as it generally
underlies the coal, whilst in Spain coal-bearing strata are
associated with it.

CAftaoMrr.aors.

This formation, so imj»ortant in its economic bearings, is a
vast assemblage of calcareous, arenaceous, ami argillaceous
strata. Of these the great masses, of limestone were probably
formed in deep seas, and the coal shales either m estuaries or
lakes, so that where the limestone division prevails, the shales
may he expected to diminish, and the estuary character being
lost, the coal will become leas abundant, as in Ireland, where
it is comparatively scarce.

The great limeatonc deposit which forma the basis of this
fgitcm has boon called the mountain limewUme, and m charao»

RUDIMENTARY GEOLOGY.

133

terixed by many peculiar fossils : in the South-wait of England,
in Somersetshire and South Wale*, it is strongly marked, and
is separated from the coal measures above by a thick deposit
of arenaceous strata ; but in the North of England the coal
descends into the millstone gri% and even alternates with the
upper beds of the mountain limestone ; and in Scotland, this
mixture of marine strata with those containing coal is still more
marked. In Ireland, many of the masses of the mountain
limestone are sejiarateil into distinct beds by shale, not asso-
ciat'd with coal, which was probably also deposited in
tohraMy deep water, as iu the Mediterranean, where the coral
living at the bottom of its waters is frequently covered over by
mud moved along by the currents.

The presence not merely of avast variety of terrestrial plants
in the coal shales and grits, but in some cases of fresh-water
fossils, has led to the belief that some of thesr deposits were
lacustrine; but whether formed in actual takes, or at the
mouths of rivers which, when occasionally dammed up, became
for the time lakes, cannot Ik* determined. The fossils of this
formation are very characteristic : in the plants, so rich in
forms which resemble the tree ferns of the tropics, there is
evidence of a climate like that of our most Southern regions,
and the analogy is supported by a great abundance of sanrtml
babes, and of cartilaginous tishc* of the families of sqtialkUc
and rminhr. The cruiouU, or lily'fthafMxl animals, are largely
developed ; as are the corals, many of which are lamelliferoua,
as in coral reefs now forming : and in investigating this portion
of the sookigy of the formation, it is desirable to study the
habitats of corals, many of which are confined to reefs whilst
others live in shallow water on Uie coast and are frequently
enveloped in mud, and thus to trace out the peculiar condition
of live sen-bottom of that epoch. Of brachiopo dona molluscs,
the genera product us and tpmfer abound.

Coal is the product of ancient vegetation entombed in mud
«od sand, and in the course of age* reduced to its present state
by chemical change ; but oooautentiy with this cgnchmioo it

SL'DUKKXTAftr GEOLOGY.

1S4

might be assumed either that the plants grew where the coal
now exists, or that they were washed down into estuaries, and
there accumulated, or that coal is the product of ancient bog or
peat moss, — an opinion supported by microscopic investigation.
It is highly probable that each of these theories is correct in
certain localities, and the alternations which must have taken
place in either case are very remarkable : for examples in. the
North of England the total thickness of the coal-bearing strata
may be estimated at 3000 feet, whereas the coal itself is arranged
in many layers or seams, the total thickness of which does not
exceed 60 , whilst the thickness of the scams varies from a few
inches toff or 7 . In the Newcastle district, counting the minute
seams, there arc forty layers. At Dudley there* are eleven, of
which one is 30 thick. In South Wales there are twenty-three
beds exceeding 1 6 in thickness, beside* many others, the
total thickness of workable cool being , equal in mans to
many hundred million tons of coal. At Mon* then* are 115
workable seam*, few of which exceed 3 thick. .Besides tbe
Irish and Scotch coal Helds, England mid Wales possess the
following coal hasins : Northumberland and Durham, York-
shire, Staffordshire, Lancashire, Whitehaven, Warwickshire,
Shropshire including C'oalbrook Dale, North Wales, South
Wales, some of which may be subdivided into other basins.

These masses of vegetable matter, composed of the remains
of plants which have long since passed from the living world,
the great** proportion belonging to the order of* ferns and
otliers being giant mosses and cellular plants, exhibit peculiar
conditions of organic life. Some of these conditions have been
repeated, though in a fainter degree, at subsequent epochs, and
given rise to limited carbonaceous deposits; but as the various
changes, physical and organic, effected on the earth** crust#
advanoe towards the present state of things, an approximation
to the conditions now observable, or a recession front those
which once so greatly promoted the growth of succulent plants,
is in accordance with tbe laws of nature. As the effect ef
a diminution of central h ea l became locally psreniptiMs. sue*

KT7DIMBNTAEY GEOLOGY.

115

cent r e portions of the earth were fitted, though in a varying
degree, for the support of such plants, and partial deposits
therefore appear at various epochs ; and it may be added, that
when the Polar regions were thus brought to a proper tempera-
ture, they were, from the deficiency of solar heat, better
fitted for stfeh vegetation, the climate being more equable
and leas affected by the scorching effects of the sun's rays
than in Southern regions. The seams are sometimes extended
over a wide space, but the geurral character of a coal deposit
is that of a basin in which the phenomenon of faults is strik-
ingly exhibited, the seams being sometimes thrown up or down
several hundred feet; some faults being accompanied or caused
by dykes, whilst in others the cause of dislocation and of
vertical slips is not visible on the surface. The knowledge of
the vsrious forms of faults, and of the direction in which a
suddenly lost seam should In* sought, constitutes oue of the
most difficult points in mining science.

The following Table from Dr. I re gives the quantities of
coal shipped from the se\ersl j>ort» in Knglaud, Wales, Scot-
land, and Ireland, in 183b and 1837, and there has since been
a vast increase, as it spears in Taylor's Tables (* Statistics
of Coal,' p. 260) that 1 1,231,730 tons were shipped in 1813.

1836. 1837. Increase.

T **<**. tom.

England sad Males 6,757.937 7.570.234 812,317 or 12 02 per seat.

Scotland. . . . 624308 626,532 2,224 or 0 36 „

lrcUad . . 7.027 7315 4W» or 6 64 „

Total. . . 7389,272 8.204301 8 1 5,029 or ) 1 03 per cent.

In Fuller** time (1661), 200,000 chaldrons were imported an-
nually into London, but now the consumption is nearly 3,300,000
tons, which is brought into port in about 9700 ships. The an-
nual quantity raised was estimated at 13,300,000 too* by Mr.
Taylor, and Durham and Northumberland, he considered, could
have met that demand for 1700 years. Mr. ft. C. Taylor
estimate* the whole British production in 1843 at nearly
SSpOOOyDOO tons per annum. The area of the coal meneun a of

136

RUDIMENTARY GEOLOGY.

Great Britain and Ireland is 1 1,859 square miles , or 7,589,760
acres, or about one-tenth of the total area ; and there are in all
51 coal fields. The French Mining Reports state that coal is
raised in thirty departments of France, in which 258 mines are
in operation, and 21,913 workmen employed. In 1814, the
quantity raised was 665,000 tons ; in 1 825, the quantity had
doubled; in 1832, the produce was 1,600,000 tons; in 1836,
it amounted to 2,500,000, and it is now more than 4,000,000
tons.

Cotta gave in 1 839 a statement of the coal produced in the
several coal districts of Europe, which is useful for comparison,
though requiring much correction, as the produce of Belgium
was in 1845 about 5,000,000 tous.

In England . .

Tam.

20,769,231

Drought forward

Tom.

30,753,233

Belgium . . .

5,215,385

1b Sweden and Norway 28,293

Prance . . .

2.215.385

Hanover . . .

21,646

Pm mia . . .

1,569,231

Spain ....

18,462

Ruaaia . . .

738,461

Doth lletac . .

13,231

Austria ** Bohemia 184,616

Sardinia . . .

4,662

Bavaria . . .

32.308

Weimar . . •

1,939

Saxony . . .

28,616

Portugal . , .

413

Carried forward

30,733.233

Total . . .

30,843.881

Mr. R. C. Taylor states the production of the United States
as about 4,500,000 tons, but this affords an imperfect measure
of the power of production, as the area of the Alleghany coal
field is tf$,300 square miles, or nearly one -fifth of (he total area
of the States in which it is situated. Dumas gave, in 1 828,
the following values of the coaljiroduced :

Ragland

Low Constrict, lariotBag EHesiah Pm- \
risers sad Luxemburg . . . . /

Prases

Uaaovsi eifd German C oo fc d e is t ioa •

Ml

Fnm.

£

90,000,000 -

iMIMO

37,000,000 -

1,464,383

12,000,900 m

475.000

3*600,000 -

134.000

3,600,000

135,000

mXTDIM*NTA*Y GIOLOCY.

137

The cod produced by the British coal fields more than
doubles the quantity raised in the collieries of the rest of Europe;
and the gross value of the collieries of Great Britain and Ire-
land cannot be estimated at less than £ 9 , 000,000 sterling.

But this is not the only valuable product of the formation.
Beds of argillaceous carbonate of iron, or clay ironstone, which
is the iron ore principally used in the British Isles, are
associated with the coal shales, thus putting in contact with
each other the mineral ore and the fuel for smelting it. In
1826, the quantity of pig or cast iron produced was between
600,000 and 700,000 tons; and in 18*16, 2,214,000, being
equivalent in value to 4?8,856,000, at £4 per ton sterling.
In Prance, the number of establishments in 18.16 was 89*1, and
of workmen 15.738, the product being 303,739 tons of pig
iron; and m 1845, 448,900 tons of pig or cast metal were pro*
duced and manufactured into 342,200 tons of bar iron, which,
at about £6 per ton, would be worth two millions tier*
ling; and as the manufacture of pig into bar iron is so closely
connected with the first process of smelting, that the higher
value of this product may he assumed instead of that of pig
iron in estimating the importance of the iron manufacture, —
how great must be the wealth produced by this homely but
most essential metal, even in this earlv stage. !u Prance, that
beautiful association of the iron ore with coal, which distin-
guishes the British coal fields, exists only very imperfectly, so
that a large portion of the iron is smelled by wood or charcoal.
In Belgium, which as a coal country ranks in Europe next to
England. 150,000 tons of iron were produced in 1845, and
most summer travellers know the busy activity of the iron
works of Liege, where 4200 men are employed night am) day,
and are aided by eleven st ea m en g in es with an aggregate force
of 500 horse-power.

Nor are these the only resources of the formation* In
England the mountain hmcstooe, which exhibits in its layers of
siliciousor chert concretions a strong analogy to the subsequent
pelagic deposit of the chalk, is the source of much mineral

188

BtrDnmrrjJtr giologt.

wealth, and produces more than one-half of its lead. The
proportion doe to this formation may be assumed as 80,000
tons , equivalent to about £800,000 sterling; so that, from
this formation alone, mineral wealth is annually produced in
Great Britain to the amount of nearly £19,000,000 sterling;
whilst, in addition to this direct production, its indirect import-
ance as affording the means of smelting the ores of other metals,
such as copper and sine, is forcibly illustrated by the extensive
works of Swansea, to which copper ores are brought from all
quarters of the globe, and the value of the lime, and marbles
or other building stones, produced from the limestone, and of
the excellent building stone which is obtained from many of its
grits, as in the neighbourhood of Glasgow, the beauty of that
city being due to the proximity of such excellent materials, is
very great. If the mind passing from the simple value of the
material* themselves can realise the vast results proceeding
from coal and iron in the use of machinery in manufactories
and railways, it discovers in the possession of such large and
productive coal formations, the source and foundation of the
commercial, and, as its consequence, the political greatness of
Great Britain.

Great Britain has in her colonial possessions of New Holland
another coal formation, which bus been supposed to belong to
a more recent epoch, though it is highly probable that the
peculiarity of some of the plnnt* only implies a commencement
of that taxation of type which now distinguishes that country;
and the coal of the East Indies is alao supposed to be more
recent than the true coal formation. China and Japan are
supposed to {tosses* extensive deposits, and coal occurs in Bor-
neo and Labuan. In America a formation both of blind and
bituminous coal, within the limits of the United Stales, greatly
exceeds in extent our British coal fields ; and in oar own colonies
of New Brunswick, Nova Scotia, Cape Breton, Prince Edward's
Island, and Newfoundland, there is an extensive coal formation.
In New Zealand coal of good quality has also been found; and
there is reason to believe that in our South African possession*

mVDIMBXTJJUr GEOLOGY. 139

ft coftl formation of considerable extent exists in Port Natal.
The preceding is but ft faint end imperfect sketch of the Intend
distribution of this most valuable minend formation, as it has
been impossible in so brief a space even to notice some of its
deposits, such, for example, as the Spanish coal district of
Asturias ; but enough has been said to show bow kurge a por-
tion of the earth's surface had been at this epoch clothed with
a tropical vegetation. The disturbances which have affected
the crust of the earth cither during or subsequent to the
formation are not only exhibited in die great faults of the coal
beds, but in the remarkable difference of position in which
such beds occur, many of the seams at Newcastle being worked
under the sea, whilst at Chipo, which rises above the Plain of
Santa de Bogota, coal is found st 8000 feet above the sea,
and at Iluanoco at 12,800 feet, or at the limits of eternal snow.

It was supposed only recently that reptiles first existed at
tbit epoch, exhibiting in the Arcbegosaurus a monstrous form
between the toad and iiiard, the body of the former being com-
bined with the jaws and teeth of a saurian, and it was further
assumed from the discovery of carboniferous reptiles that the
future discovery of the remains of birds and mammals in tliat
formation would not be impossible ; but it does not appear
that the one discovery renders the other more probable, as the
peculiar blending of the saurian and batrachian types in one
indicates a more than usual development of reptilian organ-
isation calculated to combine in one great class the functions
spread over many classes in the more balanced and perfect
organic system of the existing world. The discovery of three
species of the genus Arcbegosaurus and of the genus A patron
carried back the origin of reptile life from the permian to the
carboniferous epoch, but it has now been pushed still further
back to the Devonian by Capt. Brickenden and Dr. Man tell,
thus proving the existence of dry land and of air-breathing
animals of a similarly mixed type between the lizard and the
frog anterior to the coal deposits.

140

lVmMIKTASY OKOUWT.

nmUK t IlfCLTJDIlfO MACKES 1AM LIMUIONK.

This formation, including its underlying red conglomerates,
sandstones, and marls, is important, at it overbes the carbo-
niferous. In the Sooth-west of England its strata are udcoo-
formable to those of the carboniferous system, whilst in the
North-east they are conformable to and seem to form part of
them ; but as in all formations, cases of this partial coofonna-
bility between the upper and lower will occur, according as the
disturbing morementa are more or leas extensive or local,
it hi necessary to determine great geological divisions from
a general and not from a local examination. Though the
sandstones strongly resemble the new red sandstone, the fossils
of this formation closely approximate to the carboniferous* the
genera product us and apirifer of the hrachiopoda occurring in
both ; as well as the genus pabeoniscus of fishes, a remarkable
genus, which however extended upwards into the new red sand-
stone, where the pahconiacus catopterus occurs in profusion,
associated with posidonomya minuta, in a small patch or pool
of the sandstone and marls of Rhone Hill, county Tyrone. In
the opjKwule direction, spirifeT undulatus (8ow.), supposed a
characteristic species of the magnesian limestone, occurs in
Ireland in beds which are overlaid by apparently well-marked
carboniferous limestone. On the Continent, the name 4 rochet
todtliegendes * has been given to the lower red conglomerate,
to distinguish it from the white grits which immediately
underlie the kupferschiefer or copper slate and sometimes
contain copper ore, which the red-demf-lyer does not. In
England, there is neither the copper slate nor the white grit,
and the lower red sandstone and conglomerate axe placed by
Cotta in the carboniferous system which immediately under-
lies the magnesian limestone. In the South-west of Eng-
land, drift or conglomerate beds prevail which posam the
peculiarity of a dofomitk or magnesian limestone p as ts ; in
the North-east, a yellow magnesian limestone, yarning upwards
and downwards into marl slate and marl with gypsum. On

ItnniflKTAW OTOLOGY.

141

the Continent, the sechstera is a deuae though sometimes
porous, grey, generally fetid magnesian limestone, connected
upwards with marls containing many extraneous substances,
such as ironstone, gypsum, and rock salt, thus approaching to
the character of the true new red. The copper slate of
Mansfield has a thickness varying from If ft. to 2 feet, and is
worked in numerous establishments by a most difficult process,
called there krummholxerarboit, or crook ed- stick work, the
miners crawling and working in low cavities, only 1H or 20
inches high, lying upon their sides, and being supported by
pieces of bent timber or crooked sticks. In England, the
formation is practically important from the excellent building
stone which some of thr magnesian hods afford, the tint being
specially favourable for Gothic buildings. York and Beverley
Minsters are favourable examples of the stone, but its dura-
bility varies according as the more purely tnngnesian limestone
or the gritty bed* have been used. This stone has been
selected for the New Palace of Westminster as the best
building stone of England.

It was long thought that nothing hut deteriorated roal
would be found under the magnesian limestone; lmt this error,
doubtless proceeding from a belief that the magnesian lime-
stone, like crystalline dolomites, had lieen formed from tticta-
morphie action, has now been dispelled, and the magnificent
collieries of Iletton in 8outh Durham have laid open the erial
seams by piercing through the magnesian limestone. Mr. W.
King has illustrated the formation by his recent monograph of
permian fossil t. This monograph exhibits some esses of
approximation to the subsequent trias, but more of a close
resemblance to the carboniferous ; and it may also be stated
that the flora of the permian approximates more closely to
that of the carboniferous than of the trias, though M. Adolph#
Brongnmrt has pointed out great differences in its several
divisions. In Russia, the permian system is fully developed,
and c om b in i n g all forms of deposit, is manifestly entitled to the
rank of a distinct formation. Mr King has described 277 species

142

mtJDfMsirrABT geology.

of plants and animals, and very recently two remarkable fishes
from the Russian strata hare been described by Fischer, — the
OmmotoUmpes Eichwaldi, which b 3 feet long, and corered
by bony shields, which were at first mistaken for tortoise-
shell, and Trachelocanthna Stschesrovskii, which has a spine in
its throat turned backwards, — both of which, from their affi-
nities, were probably fresh -water fishes.

NKW SID SAKDSTONK, OS TMAfl.

This formation, from the prevalence of a variegated cha-
racter in its sandstones and marls, has been sometimes called
• poikilitic * On the Continent, where its several members
are better developed than in England, it has received the name
of 'trias,' as divisible into three great sections. The lowest
of these is the * hunter sandstein,’ or variegated sandstone,
which is distinguished by greenish stripes and spots, and con-
tains day galls ; it is associated both above and below with
variegated red and green marls, containing both laminated and
fibrous gypsum, and rock salt. The muschelkalk, or central
division, is deficient in England, and as gypsum and rock salt
occur on the Continent in marls, both of the upper and lower
division, it is difficult to decide generally whether our salt-
bearing strata do or do not belong to the more decided sand-
stones and conglomerates which underlie them. The white
sandstone of the Vosges, supposed to belong to the lower
or variegated division, is placed by Sir R. Murchison in the
permian : it is a valuable building stone.

In Thuringia and Swabia the muschelkalk division b fully
developed ; the limestone (which b occasionally dolomittc)
occurring under several forms or varieties which alternate with
marls and days sometimes containing gypsum and rock salt.

In the upper division or keuper, marls and days prevail,
though still associated with sandstooes. Gypsum and rock
salt still occur, and sometimes an impure coat Aa fossils tie
extremely rare in the sandstone dmskma, b was scarcely
possible to a ll oca t e to their proper place in this triple system

BVD1MKKTA&T OSOLOGY.

143

the Kngfah beds ; bat the fossils of a dark marly stratum
called the * bone-bed,* which occurs at Axmouth, and on the
banks of the Severn in Gloucestershire, are characteristic either
of the keuper or muschelkalk ; they are, Hybodus plicatilis,
Sattrichthys apicalit, Gyrolepis tenuistriatus, G. Albertii, — of
which it is eery remarkable that Saurichthys apicalis, Gyro-
lepis Albertii, G. tenuistriatus, have been also found in a seam
of calcareous grit connected with black shale in an equally
local deposit on the face of Ben Evenagh, at Lisnagrib, county
of Derry, the Ac rod us minimus, another muschelkalk fossil,
being there added to the list. It may therefore be reasonably
inferred that though the muschelkalk is not fully developed in
the British Islands, two members of the series, with a pace of
the other, are certainly present.

The remarkable foot prints of an animal, to which the name
chirotherium was given, should be here noticed. Various con-
jectures as to their nature were hazarded, hut Mr. Owen has
proved that they were formed by the animal which lie had
previously named labyrinthodon from the nature of its teeth,
and which belongs to the batraebian order, or is a gigantic frog.
It will be observed that in respect to this organic form an
analogy of type continues through the Devonian, the carbo-
niferous, the pemuan, and the triasic formations. The genus
ammonitei of the cephalopodous molluscs first appears here \
and in the flora as well as fauna there is a striking difference
from the underlying strata, the species of forty-seven genera
noted by Professor Broon being quite distinct. The type of
decapodous crustier a, to which our crab and lobster belong,
first appears, and footsteps of supposed wading birds have
been observed in America. It was announced some years ago
that the remains of mammals had been discovered us this
formation m Wurtemberg, and this discovery has been con-
firmed by the detailed description of the fossil booes by M.
Jiegrr, who considers them to belong to an animal of the
marsupial type, allied to the diddphts ; and if this be a cornel

144

KVDimmftT OKOIOOT.

determination, it w another example of the re ry early appear,
•ace of this now almost isolated type on the earth.

In England, this formation is the depository of rock salt.
In Cheshire, the alternating beds of red and green marl with
gypsum and rock salt sometimes exceed 600 feet in thickness;
and at Northwich, the two lied* of salt are at least 60 feet in
thickness, and extend laterally for I } mile. In Ireland gypsum
prevails more than salt ; but even there, on the line between
Belfast and ('arrickferguii, there is reason to believe that salt
may be found. And generally the curious connection of sul-
phate of lime with chloride of sodium deserves attention, as
affording a probable indication of the occurrence of salt in other
formations, and some clue to the laws which regulated its
deposition. The average quantity of salt manufactured in
Cheshire inav be stated at about 2o0,<X>0 tons annually. The
celebrated salt mines of Wiebcaka, in Galicia, belong to tbs
cretaceous formation.

LIAS GRDta.

In this formation argillaceous matter or clay prejonderatea,
being aasociatetl with argillaceous limestone, marl, sandy marl,
and sandstone, and it is remarkable as having been the age
of marine rrptilia; for although the genus ichthyosaurus first
appeared in more ancient deposits, it seems to have here
attained its hill development, and was accompanied by the
equally curious genus plesiosaurus. The existence of s
marine aauriau amidst the GalUpagos Islands, as noticed
by Dr. Darwin, exemplifies the probable mode of existence
of these vast animals, and the confortnability of their habits
with those of the crocodile. A curious genus of cephalopodous
m ollusc*, the bdrmnite, first appears here, and the grrphsm, a
genua of the family of oysters, is abundant, establishing by their
presence the manac origin of the deposit, and confirming the
faet that marine aauhaas were, at that early period, swimming
in mu l ti tu d e * mound the muddy shores of the then existing

KDIMimiY OBOLOOT.

ia

land. Hm characteristic colour of the li meet one, which tome*
timet in a section exhibits a riband-like arrangement amongst
the argillaceous beds, is blue, but there is occasionally a white
variety, whilst in some instances sandstone prevails over the
limestone in the lower members ; as for example, in Wilrtera-
berg, where sandstones of brownish and yellowish hues are
associated with marls and limestones in the lower lias, the
upper being composed of dark lias shale and limestone. The
lias shale of Wtirtemberg is so rich in a species of the genus
posidonomya, the P. Bronnii, that it has been called the poai*
(Ionian shale; and the similar occurrence of that genus in shales
of the carboniferous period, as well as in marls of the new red,
is illustrative of the analogous character of all such deposits,
Some thin beds of coal occur also tn the shales, which, as well
aa the limestones, are strongly impregnated with bitumen, the
product, most probably, of decomposing animal substances, such
as fishes, he., which abounded at the qxx*h of their deposition.
Practically the sandstones, though liable to become iron shot
or stained, are occasionally sufficiently firm to be used for
building. The limestone is occasionally hydraulic, and the soil
is generally fertile.

OOLITE OE IVtL A FOB MAT! OK .

The days of the lias form the basis of the oolitic system,
and in ascending into it, other argillaceous bands mark t ho s e
changes in the conditions of deposit which are to be expected
in every great formation, representing, a a it most do, the varia-
tions of drift consequent on the changing direction of currents.
These hands have, in England, led to a division of the oolites
into lower oolite resting on the has ; the middle oolite resting
on the Oxford day, which separates it from the lower oolite j
and the u p pe r oolite resting on tbs Kintmeridge day, which is
between it and the middle oolite i but it must be trident that
such day bands, bring merely the result of local causes, can-
not be expected to occur unteersally, or to produce a wimlar
dmrio tt in all countries. On the Continent, the format:** ban

a

146

«VDfMCfCT4ftT OEOtOOT.

been divided into tbe upper and lower Jura, tbe upper being
charartemed by a light -coloured, whitish or yellowish lime-
stone, which forms the great mass of the Jura Mountains, from
which it ha* denied its name, and the lower consisting of roe-
stone and dolomite, the Utter penetrated by holes or rarities,
and of sandstone, marl, and cUy. The hornstone partings
of the Jura limestone strongly resemble the flints of the
chalk, and its surfaces exhibit very beautiful dendritic mark-
ings of oxide of manganese like those of tbe elialk of Ire-
land. The Havanan Jura formation is remarkable for the
numerous hone caverns of its dolomites, and for the cele-
brated lithographic stone of Suleiihufea. The wooded hill*
of Psppenheim are com|>o*ed of a regularly stratified lime-
stone, arranged in thin horizontal bed*. The »Umr is extraor-
dinarily purr and denar, yellow or grey in colour, and, from the
thinness and regularity of it* layers, jieculiarlv tilted for litho-
graphy. The hills themselves are distinguished by their hrokcu
a»]K*et and wall* like character, which makes them look Ukc so
many fortresses ; ami on entenng the valleys, the ringing sound
of the true lithographic stone, as it is broken up for use, is
heard mi all side**. The layer* used for this purpose are
from I to 4 inches thick, and when still thinner, or unfit by
routaintug fossils for lithography, they become useful as
roofing tiles, as door and window linings, as tables, kc ,, to
which puqioscs they bad been extensively applied long before
the invention of lithography. Tliesc peculiarities of the phy-
sical features of the country, and of the mechanical characters
of the stone, deserve to be remembered in looking out for good
lithographic stone in other countries. The presence of large
fossils is a great defect in lithographic stones, and veins also
should be carefully avoided, as in printing they mark tbe drawing,
howe ve r flue they may be, with white lines, and increase greatly
the difficulty of reducing the surface to a uniform state. Of
the oolites the Stoueafickl slate, lying at the base of the

great oolite, a member of the lower division, is the most remark -
able z it is a slightly oolitic limestone, and only 6 fleet

KT?t»!MKNTA*Y OtOLOOY.

147

thick, abounds in fossils. With impressions of fern* and other
terrestrial plants, the elytra of beetle*, am) the remauu of
naurtan genera already noticed, occur those of the pterodactyl
or flung luard, and what is still more remarkable, ihc jaws
of at leant three npecie* of mammiferou* quadruped* of the
marsupial order, — partly allied to the opossum, and partly to
the marsupial genu* myrmecobtita of Australia, — a singular
analog) , at this early epoch, to a region still so widely distinct
in its fauna from other jiarts of the world. In the lower divi-
sion also occurs the Hath oolite, which is au excellent *tone
for the delicate mouldings of Gothic architecture, and is
represented in France by the Caen stone, which was im-
ported for the purj»ase by our early architects, as may be
seen in the beautiful Temple Church. In the middle oolite
is the **corml rag,’ so called from the continuous beds of corals
of which it is compoard, and which still retain the position
in which they originally grew. In the tipper oolite is the
celebrated Portland stone, so well known for its beauty as a
building stone.

Many parts of this system are distinguished by a profusion
of some particular fossil, a fact which is always characteristic
of a regular deposit, as distinguished from a drift : such, for
example, were the great oolite, the surface- of which is studded
over with pear-cncrmites, which were afterwards buried by the
irruption of the Bradford clay, the clays of the tipper oolite,
with their oysters and gry philes (oatrra deltoidea and grypbwa
virgula), the nemuean limestone of the Jura, distinguished by
tbe peculiar tuiirahe genus neritura and the diceras limestone
of tbe Alps, so called from the abundance of specimens of ilia
rery curious binder germs diceras.

In this formatiofi the fossils generally mark a marine origin,
but tbe frequent occurrence of fragments of wood, the coal
beds and bituminous shale which enter into the system, the
many im pressi ons of plants tod of insects, as in the calcareous
slates of Stoaeefieid and Soienhofat, the abundance of aaorians
and of encrimtes which may be cotmdered man feted for

148

tVDimmKT GEOLOGY.

shallow than for deep waters, and, shore all, the actual dis-
covery of U**d animals, which it k now known existed even in
the tries, all coocur in proving that the deposits were formed
in the vicinity of land ; and it is therefore a fitting pre c urs o r
of the next formation, in which evidences of land and fresh
water in connection with it are more decisive.

WEALDEN rOEMATfON.

This formation, remarkable for its fresh- water origin, it not
entirely destitute of marine fossils, and it has therefore the
character rather of an estuary than of an inland lake. On the
Continent, it has been associated with the cretaceous system,
and considered the equivalent of the Neocomien of the French.
In England, the oolitic beds were first raised up quietly with-
out any great disturbance, as is shown by the celebrated
'dirt-bed* of Portland, with its upright roots, which rests
horisontally upon them, the roots even penetrating into the
subjacent oolite; and then portions of the compound deposit
were thrown out of the horuontal position, as appears in
the section at Lulworth Cove. If the principal basin, in
which these beds have been traced, extending at cadi end from
France into England, be really continuous, the deposit, whether
lacustrine or estuary, was Terr extensive, though much inter-
rupted, formations of a different character being contempo-
raneously deposited within its area : hut these are problems
very difficult of solution, as it is almost impossible to repre-
sent to the mind the actual condition of the earth's surface in
respect to land, sea, and river, at each successive epoch of ha
history, obscured as it must have been by the effects of re-
iterated changes and unceasing wear.

This vast lake or estuary being exposed to the action of the
sea, the dry tend bordering it, and islands within its precincts,
were covered by the marine deposits of the cretaceous epoch,
an operation which wes aided by a depression of the land suffi-
cfent to p er mit dacp sea deposits. 8och wonderfal oadBattons
are strongly con tr as ted with the c omparati v e quiet which new

mumMKKTAEY OKOLOQY. 149

reigns on the earth j but they are learnt from geological in-
vestigatione, just as the fects, the habits and opinions of past
ages are from historic records ; and we owe therefore to this
science the knowledge we now poems of changes which must
without it have been unknown to us. In England, where this
formation is more externa rely de reloped than in any other
country, the well-known Purbeck limestone, distinguished by
s profusion of fresh-water shells, forms its base. The lx*d* of
limestone are serrated by marls, and the conjoint thickness
is about 250 feet, a great depth for a freah-water deposit.
The Hastings sands with clap and calcareous grits succeed,
and are about 400 feet thick, being equally extraordinary as
a freah-water drift ; and the whole is covered by the Weald
clay, with iu thin beds of sand and shelly limestone, about
200 feet thick. This formation implies the existence for a
long time of vast areas of fresh water, resembling those of
North America, in which at this moment, from the conti-
nued wear of their hanks, and depth of their bottom, which in
some cases is below the level of the sea, extensive deposits
must be forming. Mr. Robertson has proved the existence of
Wetiden beds st Brora, in Suthe rlandshirc, and advanced rea-
sons for associating the Yorkshire oolitic coal also with this
formation. The Neocomien beds, which French Geologists
consider the equivalent of the Wealden, are marine deposits
consisting of variously coloured sands, and of marls and
dap characterised by peculiar fossils, amongst which especially
Holaster complanaiua, one of the Ediimdsc, abounds. These
beds are separated from the overlying greensand by French,
and associated with them by English Geologists.

S imilar freah-water deposits can be traced in other countries;
and it » evident therefore that a very large portion of Europe
was once covered with fresh water. In Westphalia the Wealden
k represented by a deposit £00 feet thick, consisting of sand-
stone wad bituminous marl, with layers of coal and of ironstone
and beds of fcmertooc, the whole bcutg characterised by fresh-
water foamb. In Saxony, at Ntedcrscbta* it k reduced to «

150

KVDIMENTAftY GEOLOGY.

deposit 40 feet thick, of dark-cokmml sandy shale and mart,
which is sometimes bituminous, and contains traces of coal, with
an abundance of vegetable remains. Amongst these foaail
plants only one shell has hitherto been discovered, but that is
a most characteristic one, belonging to the frrsh-water genus
anodonta, which is confined exclusively to muddy lakes and
pools. The quadcrsandstcin, or green-sand, overlies this de-
posit, and Cotta thinks it prnliable that the beds of that forma-
tion in Silesia, which contain coal and the remains of plants,
should also be allotted to the* Wcalden. Amongst tin? numerous
reptiles of this q»och appear tortoises of genera which now
occur in the fresh water of tropical regions. The iguanodon,
so called by its discoverer. Ihr. Mantel!, from its analogy with
the living iguana, was a herbivorous reptile about .10 feet long,
and appears to have abounded at this epoch, associated with
the hylwoaaurua, another gigantic saurian. The nature of the
foaail plants, and tin* number ami magnitude of the reptile*,
show that the climate still continued tropical. The Furbeck
limestone is well known as lumachella marble, the designation
lumarhella lieiug derivrd from the Italian word litmaem, a snail,
and applied to those varieties of limestone which, with a gra-
nular or marble structure, abound in fossils Caution is matured
in the selection of tins stone, as some of its 1ml* easily disin-
tegrate ; ami ui all sjieoticatious for its supply a sample should
be referml to, in order to insure the delivers of the proper
kind ; a remark which »# applicable in various degrees to almost
every building stone. The sandstones, which are not durable,
wear into very picturesque scenery, as about Tunbridge. The
clays produce a strong soil, as in the rich district of the
Weald of Kent.

Before quitting this last member of the oolitic aeries, it is
right to make a few general observations on the farts which
it exhibit*. The wet of the oolites was one in which the
reptile type was most highly developed ; and reptiles, from the
first appearance of the type in the old red sandstone, or pro-
bably in the Silurian, to its condition of highest dewdopnmni

RUDIMENTARY GEOLOGY. ]£]

in the oolite*, appear to hare been designed to fulfil the func-
tions of other claaaes of animal*. Hence there is a variation in
the anatomical structure calculated to embrace forma and func-
tion* now appropriated to other animals. In Australia this ex-
tension of one type so a* to represent several classes of animals
is found in the marsupial*, some of which are herbivorous, some
carnivorous, and when it it considered that the saurian* of this
epoch peopled at once the seas, the land, and the air, wc may
reasonably believe (hat they represented in great measure other
classes, and that there is little reason to believe that any great
number of other mammal* or of birds then existed. The
association with them of the mamipial type, which exist* so
isolated in Australia, is rather confirmatory of this view tlum
otherwise ; and the occurrence of coal iu the Yorkshire oolites,
as well as in the East Indies and elsewhere, is another proof
that the general condition* of the earth were still fitted for the
rank and luxuriant veprtatio n of those early ej»orhs, and for
the existence of multitudes of huge reptiles, against which Man
in bis primitive stale must have contcuded in vain. The earth
wa*. in fact, progressing toward* a fit state for Man's residence,
and the animals which lived at each stage were perfect in their
kind, and suited to the conditions of the epoch.

CRETACEOUS.

Succeeding to the extensive fresh- water formation of the
Wealdeu, is a still more extensive, and generally more widely
diffused marine formation — the cretacrons. This change is
similar to that which will take place if, alter the long -con tinned
deposit of fresb-wairr detritus in the depths of the lakes of North
America, the sea shall he admitted by a depression of the aur-
hcr, and the bottom of the lakes now actually below the sea
level shall become a sea bottom. Even a moderate depression
would cause such an irruption of the sea over ft large portion
of the country, and manor depoait* would immediately com-
mence. If, again, after an aocumulaiioa of such depcctta,
Mgahraleai in thick oeas to the cretaceous, the whole mats were

152

kVDtVINTiKT OKOLOGY.

uplifted b y the action of subterranean forces, tike fresh-water
deposits might be brought to view by the fracture and remoral
of part of the marine covering, of which the remaining part
would continue ai a mural boundary surrounding them, and the
result would be analogous to the Wealdeu and chalk. Com-
mencing at its base, the cretaceous system is sandy, and this
division has been named the green-sand formation in England,
the quadersandstein formation in Germany, — names derived
from the principal peculiarity of the sandstone in each locality.
In each it admits of further subdivision into upper and lower,
the two being separated in England bv a deposit of marl and
day called gmult ; in Germany by one of marl, marly sandstone
and limestone (the plinerkslk). But though these divisions
exhibit a striking conformity when viewed at particular locali-
ties (if, for example, the green sand of England be compared
with the quadersandstcin of Saxony and Bohemia), considerable
modifications appear in other localities, in Westphalia and
North Germany, a conglomerate and a clay which Cotta con-
sider* the equivalent of the Specton clay occur below the lower
quader : the planer is replaced by a blue day with crystals of
gypsum, corresponding still more closely with the English
guilt i the upper quader is represented by a green-sand, which
is surmounted by bright and red marl. The sandstone of the
Carpathian Mountains is also refemblc to this epoch. On the
Continent, the upper limit of the green-sand is not always dis-
tinct, as the same lithological character, in sandy marls and
sandstones, extends in Westphalia and North Germany high up
into the upper section of the cretaceous system ; hut these are
only natural variation*, being the necessary result of those local
peculiarities which have already been so frequently adverted to.
In England, the upper section of the cretaceous formation can
be divided into the lower chalk without Hints, and the upper
chalk with Hints, the whole reposing on the chalk marl, — a
eubdi vision which is purely local. In Saxony and Bohemi a,
the whole section is r e du ced to beds at Hints ; hi Westphalia
ano norm tserauy, me upper mem per is »eeoiy icprmssm%

Mvmumnrkmx geology . 153

bat all below it consist* of chalk marls and sandstone*, far more
is character with the green-sand than with the chalk, of which
it is proved to be equivalent b y fossils. In Prance, the Maas-
tricht beds resting on the white chalk with flints are at the sum-
mit, and from their peculiarities have been considered by some
Geologists an upper member, approximating the chalk to the
tertiary strata, though their fossils are those of the white chalk,
and the chalky character is carried downwards into the green-
sand. All these modifications of lithological character must be
anticipated by the Geologist, and his skill alone can disperse
the obscurity which they occasion as he traces out the boundaries
of sea and land, of bay and ocean, at each successive epoch.
Sometimes indeed the mineral conditions remain unaltered from
one geological epoch to another, as is the case in the Mediter-
ranean, where the Scaglta or white limestone with its flints has
been in part deposited during the oolitic, in part during the
cretaceous, and probably in part during the tertiary epoch,
unless there he a transition member between the chalk and
tertiary formations.

Few phenomena are more striking, or hmve engaged more
attention, and excited more speculation, than the occurrence of
long lines of flints in chalk ; the marked contrast between the
dark hoc of the flint and the pure white of the English chalk
having attracted special attention to chalk flints. The occur-
rence of stbeioos nodules similarly arranged is not confined
to the chalk, but is observed both in the mountain limestone
and in the oolite ; nor is the arrangement by nodules always
the prevailing one, as in the chalk of Ireland extensive layers
or .beds are very c omm on, and again in the oolitic and ore*
taccons portions of the white li m esto n e of the Mediterranean.
The origin of flints has excited much speculation, though
from the preceding observations it is evident that the question
doe* not refer to the chalk alone. A microscop i c exami-
nation having shown that they contain numerous infusorial
resanins, Ehrenbcrg was disposed to oonmder that they had been
farmed almost eschmvsly o ( each animals; whilst dm fa*
G 5

154

ETfOlMKlfTAftT GIOLOGY.

eorery of the texture of sponge in dints has led Mr. Bower-
bank to ascribe them exclusively to a spongeous origin ; and
again, other* are more inclined to believe that the silica, haring
been held in solution by thermal waters, was deposited in a
gelatinous state and enveloped the sponges and other bodies
it contains. It is highly probable that all these causes hare
contributed to produce the result ; and considering the peculiar
affinity of silica for organic substances, there can be little doubt
that sponges hare materially, though not exclusively, contri-
buted to the production of chalk flints. As yet, the comparison
of flints and cherts in various formations has not been fully
carried out, hut it may l>e assumed that they will exhibit a ma-
terial and characteristic difference in their toological remains.

The cretaceous system is peculiarly rich in fossils, the whole
mass even of the white chalk, as has been shown by Professor
Ehrenberg, swarming with infusoria and other microscopic
animals, in addition to the multitude of those of larger dimen-
sions, as echinida, cephalopoda, &c. The spongiadir and
aleyonidie are abundant : of the crinoidar there is the peculiar
genus marsupites ; of the echinida, the genus ananchytes, and
a profusion of species of many other genera ; of the mollusc*,
generally, the remarkable genera hippo rites and mdiolidet,
which with caprina, Ac. formed extensive hanks or reefii in
the errtacean tea, deserve special attention, as their true
nature is still doubtful: the genus spondylus (pUgkwtoma
and podopsis) has a very characteristic species in piagiostoma
spinostrtn ; the genus peeten affords in P. quadrieostatus and
P. quinquecoatmtus the type of a new genus, rbynchonella :
the genus inoceramus abounds; whilst of the cephakfMV
dous division there are many most characteristic genera and
species, such for example as the genus turrilitcs, a cham-
bered shell with an external tnrreted form, the besutxfal
genus bacuhtes, which unites a straight form with the sinu-
ous septa of the ammonites, the book -shaped handles,* and
a great number of ammonites and naatih, produc in g in this
aaa order an assemblage eo stsangeiy di flkwnt from that of our

IVMMtNTiftl OKOLOOY. 15$

promt tropical teas, where the single genus nautilus alone
remains, as justly to excite our admiration and surpriae. In
fish there is a nearer approach to the existing epoch, as the
genera squalus, galeus, and iamna occur; of reptiles, there is
the peculiar genus roosossurua, as well as the pterodactyl or
flying liiard. In the flora the cretaceous approximates more
closely to the existing epoch, as fifty-one species of dicoty-
ledonous plants have been discovered in the quadersandstein
of Silesia, some of which are nearly allied to the very common
genera willow and maple.

Practically, the chalk hills are well known for their smooth
outline and surface, and for the short herbage of their downs,
so fitted for sheep pasture, whilst the marly beds of the
lower portion of the system have long been known for
their fertility, as noted by White of Selbomc, In countries
where the chalk is more indurated, and resembles the oolites,
as in Greece, the tame character of its hills is changed to
a far more bold and striking outline, resembling that of
mountains of quarts rock. Chalk is valuable for lime, being
easily worked and burnt, and, though sod, can be used as a
building stone , but the while limestone of the Mediter-
ranean, which belongs partly to the chalk, is an excellent
building stone, though, being hard and brittle, dangerous in
military buildings exposed to cannonade. Flinty made up
into a species of concrete, and strengthened by stone quoins,
were extensively used in the walls of ancient churches, and arc
still so applied ; tliey are also used as a road stone, hut hr ng
extremely brittle, and breaking into fragments with sharp cut-
ting edges, cannot be oonsuleml well fitted for such a purpose.
Of the lower part of the system, the green-sand or quadev* mi-
stein m more practically useful on the Continent than it is in
E ng l and , though the soil proceeding from it is much less fertile.
In Saxony, the quadersandsteiu—to called from its breaking
into quadrangular portions—- is celebrated as a building atone,
the colour being pure and good ; sod as the planer (or ganft)
u mostly deficient -p- 4 — — n^ir*

156

RUDIMENTARY GEOLOGY.

in contact, and each yields its valuable bed of building stone.
In other localities the position of the planer is marked by a
line of water springs which it throws up, and taking an unusual
development, it stretches up into and occupies the place of the
upper cpinder, which is there wanting. The boundary hills and
the bottom of the valley of the Elbe at Meissen are of granite
and syenite ; and at Dresden a depth of 856 feet was bored
through without arriving at the granite. If this accumulation
of cjuadersandstem and pUnerkolk could he removed, and the
basin containing it laid bare and then fdled with water, the
bottom of the inland sea thu* formed would l>e more than 500
feet below- the present sea level, and die surface of its waters
about 000 feet above; hut as the sandstones and limestones
were a marine deposit, it nj»j»ears that after an cjMxh when in
not very distant countries lam! plants were growing, and an
extensive fresh-water dr|»osit forming, this basin must have
been depressed more than 000 feet below its present level,
ami have been n deep lndlow m the sea; another of the aur-
prising results, like that of the Wealden, which geological
research has made known.

In America the upper chalk is represented bv l>cds of sand
and clay totally unlike tins portion of our English cretaceous
►vstorn. The lossils, or in other words the jtoologv of the beds,
is however a sufficient proof of roiitrm}>nranetY in epoch , and
here, as in the existing ejKH'h, local mineral variation is found
connected with a general fauna. One of the most remark-
able fOologieal facts of this formation it the great development
of the auirnonidar, which ap{x*ars the result of some great law
of nature. In the Silurian e|w*ch the uautilul« appear to have
arrived at their stage of highest development, exhibiting every
variation of form, as the straight in the orthoceratitcs, the ob-
lique, the open, \c , and then suddenly diminished, though the
type is continued m our present fauna. The ammonidar, on the
contrary, commenced with the uiuschelkalk of the triaa in the
genus cermtitea, or perhaps with the gonuflites of the carboni-
ferous, flourished in the oolites, and Anally attained ihcv full

RUDIMENTARY GEOLOGY.

157

development in even' possible variation of form in the cretaceous,
where they appear for the last time ; the straight ammonites or
haculites, the crooked or hamites, the open w hurled or crioccra-
tites, the obliquely whorlcd or toxaceratitcs, the tumbles, and
many others, (massing away from the organic world for ever.

This history of the ammonites, when compared with that of
the nautilidir, induces a belief that the type of nautilus must
have commenced at still earlier epochs, of which as yet no
zoological evidence has been attained.

TERTIARY CLASS OF FORM AT I ON*.

At this period of grologiea] history, the present order of
creation may be said to begin, as the remains of ummal s|>ecies
which still exist are blended with the relies of the extinct.
Sir C. Lyell has adopted this combination a* the groundwork
of his classification, and imcntcd terms to signify, as it were,
the dawning and gradual progression of the existing creation;
his subdivisions depending on the proportional uuiiiInt of
existing species in each, a principle of einssitieation which,
though beautiful, recpiires to l>e applied with much caution.

Co-operating with M Dcshayes, tbe we ll known Trench rem-
eiiologist. Sir (\ Tyell inaturrd ins plan from an examination
ot alwiiit .ilMMI n pee us of tossil shells, and their comparison with
about otttHt hung species by M. Deshay cs, and exiiduted the
nundH*rs of recent species in eac h illusion, as below : —

Newer P horror of Sicily DO to | xr rrnt.

< >hi«r Pl»»*ri*e, or Sub Ajxnnmr to uU ,,

Mum for of (hr Loire »o«l Liromic . 1 #

E or ear of Loruion am! Pan* „

the distribution of the foaads submitted to examination having
been,

fliocrar, o44err aid msw . . . 777

Si tocetnc . . . . . 1 02 1

E'Jtnn! UAH

Sir C. Lvcil, in the 3rd edition of hii Manual ( 1 N5 1 ), further

160

RUDIMENTARY GEOLOGY.

as, for example, in the Bar of Bengal, in the East of North
America, and in Equatorial America, &<\; so that in almost
even* part of the globe traces have l>een found of that gradual
approximation to the present physical and zoological conditions
of the earth’s surface which is learnt from the study of tertiary
deposits. In a few Northern localities, it is sup|Kwd that a
tendency towards a colder climate can be traced within the later
tertiary epoch ; but generally the chmate npjicars to have con-
tinued nearly tropical.

EOCENE.

The English tertian deposits are fery local, and only impor-
tant in the lower mrnibcra. The hasms of l»ndon and Hamp-
shire are the lowest geologically, and belong to this peril h 1.
They are Ixmmled and underlaid by the chalk, and their strata
consist of sands, class, and gratcls. Comparison lielswi the
French and English tertinne* has shown that the eocene dc|K>-
sils may he subdivided, and that the upj»er jMirtioti i* deticient
in (treat Britain. whiUt the middle subdivision includes the
fresh water beds of Hampshire, and the up|>er sand or Bagshot
sand, and the lower the I*ondnti clay, and the plastic clay
which consists of alternating beds of dav, sand, and shingle,
peculiarities which, though local and not accompanied by any
im}w»rtnnt xixdogical differences, are within these districts of
great practical use, as will Ik* seen in treating of t hr subject of
' Springs.' There are several shells, such as nautili, \c., of a
tropical type, and many plants also, more than seven hundred
of winch have been discriminated ; and again in the reptilea,
the teeth and bone* of many crocodiles and turtles, and even
the i tones of a Urge serpent, have been found. Tlie remains
of a bird, of varum* quadrupeds, and of a monkey of the genus
maracus, l>ear also testimony to a warm climate.

Tlie deposits of the Baris basin are very different in mineral
character from those of the London basin, though connected
with them by soologicai evidence. Tlie "London and Bognor
day beds, which art so remarkable in the London basin.

Rl' D1 M K NT ARY GEOLOGY.

Itil

have Wen associated by Mr. Prestwich with marine shelly beds
of the lower portion of the Paris basin, and the Knglish plastic
clay and sands with the sands, plastic clay, ami lignite, of the
base of the French system; whilst the Pagshot and Prnch-
lesham sands, the Poston beds, and the fresh water atul tluxio-
marine Im'iIs of the Pie of \\ ight, llnrdwcll. \e. correspond to
the silicions and fresh water limestone, the marine raleaire
pros'ier, the marine sands am! sandstones, and the fresh water
limestone, marl, and g\ psum of the middle portion of the Paris
hasui , the Fontnmhleau sandstone and the* upper fresh water
limestone, marl, and siheious millstone liming, ns it is sup-
posed, no cipiix alents in the London hasm. Tlie eele hrnted
Montmartre g\ psiim quarries were the classic ground of the
great ('uwer’.s wonderful researches and discoveries, The range
of the London cla\ has hern extended through a large portion
of the N.K. of Luropr, h\ Dr (itrard, of Pcrhn. In other
countries the variation ot mineral charm ter is run more strid-
ing, indicating a still greater variation id the condition* of
deposit In the Mediterranean Islands tin white limestone
ranges without am marked pin sienl diiTcrencc from the oolite
epoch up to tin* lower tertian ineliisiu*, and in the I'nited
States the eocene l>eds arc* in part repre •ented h\ soft ehaikv
limestones, exhibiting e\en the external physical rhnraeter*
of our chalk downs. A gigantic cetacean, called l>\ Owen
zetiglndon, occurs in tin- upper beds, and multitudes of
orhitoidc.*, a fossil resembling nummuhtes m form, in the
lower.

The great mineral difference in these deposits in the tvro
liAsins leads to similar differ** urea of prat dial application.
Tin I<ondon rla\ beds sometimes aLujnd hi calcareous noduira,
used f‘>r making Roman cement, wbub often contain marine
abells, the remains of turtles and fruits , and when traversed
bx' cracks and veins dni lmg the mass into parts, as bv septa,
are called septaru Harwich and the Isle of Sheppv are welL
knosrn locmittira of these nodules. In the Pam basin, the
Cftkaire grower furnishes, in some of iU sarieties, very good

102

RUDIMENTARY GEOLOGY.

building stone, and the silicioua fresh -water deposit yields an
excellent millstone.

MIOCENE.

The miocenr ejmch is represented in England by the lower
portion of the Suffolk crac, which is subdivided into theeoral-
lino crag below and the red cmg alicvc. The coralline crag is
very local, an<l is generally calcareous and marly, being a ina^s
of shells and small corals, whilst the ml crag is a highly ferru-
ginous grit. Although the thickness of both members of this
deposit is wry small, not together exceeding f»0 or “0 feet, the
miiidwT of fossils is vers great. Mr. Seariex Wixxl has obtained
•J.'IO species of shells from the red erag. and .'U j from the
coralline, l .'*0 of which were common to both. There is a con-
siderable difference in the proportion of remit shells in the two
divisions, and as the lower had been disturbed before the
de|H»>ition of the upper, they exhibit a striking modification
consequent on the change from a coral reef to a shingle bottom,
an example which shows that coral reefs are not necessarily of
great thickness, the product of almost infinite ages, or that
they rest on the peaks of submarine volcanoes ; since now, as
in the ancient « growth of coral may have commenced

on a sand or mud hank, haw been interrupted bv a new dejwimit
of a similar kind, and then again renewed, such alternations
being frequent!* observable in the carboniferous period. The
faluns of Tmtrainc, the Bordeaux Iwxls, the sands, marls, and
conglomerate of Piedmont, and part, at least, of the molasat of
Switjerlaml, U long to this epoch.

Pmcticalh, the formation varies in importance in different
districts, in Suffolk, the coralline crag yields a soft building
stone, and the marls are useful as manure. In the Styrian
Alps, limestrues of a coralline and of an oolitic structure are
largely developed, and the molaase, from the ease with which
it is cut, is also valuable.

0

rUOCENl FORMATIONS.

The lower pliocene includes in England the celebrated r*d

RUDIMENTARY GEOLOGY.

m

crag of Suffolk, so remarkable for a great quantity of copro-
lites and highly phosphatitcd bones. Much different of
opinion still exists as to the true age of this dejmsit, which,
from its physical character, must be considered an aucieut
drift of beds. Although many eocene fossils occur, the asso-
ciation with them of recent forms makrs it difficult to con-
ceive that this is not comparatively a recent formation. The
red crag of Norfolk belongs to the newer pliocene, being more
recent than that of Suffolk, and it is unnecessary to dwell
longer on the upper or newer pliocene formations, which are
very feebly represented in the British Islands, bring confined
to minor deposit* of sand, gravel, and clay. On the Confluent,
however, they nrc very largely developed, extending in Sicily
over nearly half the island, and attaining an elevation of .MMM>
feet, being composed partly of calcareous and parflv uf argilla-
ceous strata, and exhibiting by the occurrence of recent species
of shells amidst such a mass of stratified matter, a striking
proof of the accuracy of ecological reasoning as regards the
older formation*. In Italy, the Sub-Apennines range from the
mioeetie up to the newest plmecue, affording a striking exemplifi-
cation of the great development of these comparatively reerut
strata, ami the blue cla* of the Mediterranean, rising sometimes
to the height of HUM) feet above the sen, is also of this epoch.
The thickness of the Norwich crag, consisting of sand nod loam,
and considered mi estuary deposit is small, afMntf in feet, and
the Suffolk crag belonging to the older plmmir is al*o insigni-
ficant m its vertical extension. In Sicily, the newer pliocene is
a rant marine deposit, but in Uus&ui there t* an espial extension
of fresh-water deposit*, a vast mass of argil lace* ms limestone
around the Caspian, which Sir H. Murchison rails the Aralo-
Cajpum, or Steppe limestone, containing univalve shells of
fresh-water origin associated with bivalves, which are common
to partially aahne or brackish water, but without roralt. The
thickness of this supposed member of the pliocene t% tn some
places between K I ami 300 feet, and it attains elevations of
700 fret above the present level of the Caspian. In like man-

164

KVDI

IT GEOLOGY.

Her the tertiary at rata of Vienna correspond to the London clay
at the base, bat merging at the top into the pliocene in-
cludes a fresh-water deposit of limestone ; these beds passing
into the more northern or Russian deposits. It is remark-
able that whilst the species of testacea of the newer pliocene
formation were nearly identical with those of the existing
period, there should still hare been so marked a distinction in
the animals of a higher class, as is proved by the bones of the
rations celebrsted bone raves and ossiferous breccias of all parts
of the globe, a difference which continued even beyond the
limits of the pliocene. It is also remarkable, that whilst in
the Old World (though animals of a high order now conhned
to warm climates extended far northward of their present
limits) the general type of extinct organisms conforms to that
of animals still existing, the type in Australia now peculiar
to itself, though Kuroj>eaii in the oolitic period, assumed its
distinctiveness in the tertiary period, that vast region haring
even then been isolated from the rest of the world.

The connection of the ancient lavs currents of Auvergne with
the tertiary strata requires a few additional remarks. The age
of the stratified dcjtosit* of the country is considered by Sir C.
Lyell to hr generally eocene, although some portions may pos-
sibly extend upwards to the nnocene, whilst the base of the
system is granite, and therefore either eruptive or metamorphic
of a more ancient date. £ir C. Lyell describes successive
gravel beds, the alluvions of different ages, covered by lavas,
and joints out that the lava curreul of the Puy de Tartaret
has passed over a red sandy clay, rich in the bones of mam-
mals, which are associated with those of reptiles and of birds,
and with several rtcmt land shells. The bones, though closely
allied to those of recent species, are considered distinct, ami
include the fossil horse of Owen. 8ir C. Lyell, from the
superposition of the lava, is enabled to affirm that the bone
beds, in whatever way the animals* were destroyed and their
relics so imbedded, belonged to the alluvial formation* of the
river bed and river plain at the time of the iowing of the lava

RUDIMENTARY GROLOOY.

m

ofTarUret; whilst he shows from an ancient Roman bridge,
not more recent though probably older than the fifth ceuturr,
which spans with its two arches the river Couse and abuts on
both banks against the lava which had thus been cut through
and formed into the present existing ravine fourteen centuries
ago, that the lava of the Puy de Tartaret was, as respect* the
events of human history, of great antiquity, and referrible
either to the close of the newer pliocene or to the post -pliocene
period, a period when “ the mollusca were identical with those
now living, although a great many of the mammalia belonged
to species now extiuct." This recurrence of alluvions and even
of ossiferous beds, with overlying streams of lavs, deserve*
especial attention, as it is utterly impossible to reconcile such
repeated volcanic eruptions to any one catastrophe.

The beds of sand and gravel spread over so large a portion
of the earth have always attracted attention, ami for a long
time were ascribed to the passage of diluvial waters over its
surface ; but a ngid examination of the peculiar characters of
these deposits has shown that such an opinion is untenable :
for example, they sometimes consist of deep beds of sand, sepa-
rated by fine clay partings into a multitude of bed* ; sometimes
they are composed of alternating layer* of sand ami gravel,
which exhibit cross lamination ; sometime* they consist of clay
with imbedded boulders of various rock* and of various sues,
the term boulder being properly applied to rolled or rounded
masse* , sometimes they coutain marine shell*, sometimes bones,
and sometimes they extend over Urge *pacrt and oerur at great
altitudes and of great thickness, without any trace of organic
bodies. Many marU and days or silt, with Und and fresh-
water shells, belong to this di« ision. When the various circum-
stances attending such deposits are rrmttdrrrd, it is evident
that they cannot be ascribed either to one great wave or to the
rush of tumultuous waters, continued only through a very
limited time. The substances of which these deposits consist
haring hero broken up> triturated, and moved by water, the
term drift has been applied to them ; but though all thtaa tab*

166

AVDXMSNTAKT GEOLOGY.

stances have been more or lew drifted, their distribution has
been modified by many local peculiarities, giving rise to deep
deposits of sand in one place, and to long continuous banks or
shoal* in otliers, just as in recent drift the sounding lead testi-
fies that such modifications are now taking place. The great
* erratics,’ or those large angular masses of rock which often
rest on the surface of sand or gravel, arc rightly separated from
the l»eds on which they he and distinguished from the rounded
boulders connected with these beds, or with the day which has
accumulated in hollows of the e arth’s surface : they are now
generally lielieved to liaw* been transjwirted by ice, as frag-
ment* of rock are now drifted along on icebergs. In Northern
Sweden the phenomenon of drift is strikingly exhibited in long
trainees, whilst the rock* are worn dow n m undulating surfaces,
and sometimes exhibit rounded northern and abrupt southern
sides, corrc»|H>»dmg to the wearing action of such loose mate-
rials in progressive motion.

Without entering into details, it may l>r generally remarked,
that the superficial detritus, so long called diluvium, exhibits
itself in several distinctive phases. I. As deep l»rds of sand,
not heaped up in one mass, but manifest h dejmsited in suc-
cessive layers, and which though doubtless triturated by the
action of water, and even mused along b\ currents, are com-
paratively Irnmpii! and regular deposits. *. A# hut's of gravel
and of gravelly clay, with rounded boulders whic h sometimes
surmount the more quiet deposits, and by their definite direc-
tion in such trainees for cien hundreds of miles, iudicate the
action of currents moving in Northern Europe, in a slightly
divergent direction from the Scandinavian Mountain* to the
south on the one hand, and from the south to the north on the
other ; indicating that the transport was not effected simply by
the usual submarine currents do wing from north to south, bat
partly, at least, by undulations of the bottom, which caused
powerful wares of translation in All directions from the axis of
disturbance. 3. As * erratics , 1 or large angular blocks, which
are not immersed in beds of sand, mud, or gravel, bat rest

RUDIMENTARY GEOLOGY. 16?

on their surface, or on ridges of rook where there is no super-
ficial covering ; and it has been hitherto considered that moa;^
ice is the only sufficiently satisfactory cause of the translation
of such masses, which, having preserved their angles, cannot
have Wn exposed to the rolling action of water. 4. in the
preceding eases, the detritus is supposed to have travelled from
A distance; hut it is very often partly local, ami then is pro-
duced by the wear of the adjacent rocks, either bv the <l»rect
action of the sea against them, or by the attrition of fragments
when moved by the tidal wave along a coast or a hank. Where
both forms of detritus occur, it is difficult to discriminate be-
tween them, or to determine which is the undrrlnng or over-
lying lied. 5. The connection of the boulder formation, and
the phenomena of erratics with ice ns a motive agent, wins
further supported by the fart that faith in the old mid new
worlds thev art* observed ntdv in repons where the effects of
extreme odd nmrht 1m* looked for, the boulder formation hav-
ing mi Europe liern traced .southward to the .'«• of latitude, and
in America to the ;$h{ , where it is «»cc nstoiuiily more than *0U
feet thick and bear* on its surface * mat tea/ mailing m size
those of Kurofw, a block of greenstone UMJ teet m circum-
ference having been noticed bv Sir ( . Lvcll, whilst the largest
European erratic on the Island Fohneti measures -It feet
across; and further, that having ceased within the tropica,
such appearance* are again observed on approasiimg the
Antarctic zone. The surfaces of rocks, when Uni hare, are in
America as io Europe striated, furrowed, or smoothed, and
as these phenomena extend from the northern elevated dis-
tricts towards the south, they required a general force, such
as that which now effects the transmission of the I'olar
waters to the Equator, and cannot lie explained by the waves
of pulswtum consequent on elevating forces alone , for though
to the north of the Hcandma* ian chain the ‘erratics* have
moved to the northward, their extension in that direction
has possibly not been tram! sufficiently far to remove them
from the possible action of glacier*, which it ia reasonable to

168

RUDIMENTARY GEOLOGY.

am me mutt have co-existed with the floating sheet and berg
of ice, and co-operated with them and with marine and lake
currents in transporting fragments of rocks by land and tea.
6. On examining the scratches and grooves on rocks it seems
scarcely possible to doubt that many of them hare been pro-
duced by pebbles moving with and immersed in the bed of
l>oulder clay which once covered the rocks. Various causes
have been assigned for this movement, such for example as
land-slips, the saturation of masses of detritus and their descent
as semi-fluid mud down the slopes of mountains and along val-
leys, and lately coast- slips of matter below the tidal line, a cause
suggested by Mr. R. Mallett, mho considers it sufficient to ac-
count even for the movement of erratics i but whilst to each of
these causes some |>eculi*r local effects may be ascribed, neither
can be considered sufficient to account for the more general phe-
nomena. The mud, sand, and gravel along the coaat is doubtless
often put into motion, sometimes bv the tidal wave producing
wear, polishing and grooving in lines jmrallel to the shore, and
sometimes in consequence of the sudden removal of its support
in deep water by the excavation of its bed by currents when
the short detritus sinks in and moves perpendicularly out-
wards ; but in these cases the moving matter is in a semifluid
state, and can neither be expected to earn’ on iu surface large
bodies, nor hold fast in its grasp the angular fragments which
scratch and groove. The only condition in which such effects
may be ascribed to the movement of a solid bed of clay and iu
imbedded angular fragments, is when the mass is retained in a
compressed and Arm state by superincumbent pressure ; and
there can be little doubt that the accumulations of mud and
oilier detritus which have been formed in the deep r ec e ss e s of
the ocean, and so consolidated by pressure as to support the
heaviest fragments, are often broken op by the convulsive
deration of the sea bottom, and by a change of iu level are
put into motion and gradually slide along the inclined plane
thus formed, carrying forcibly with them the sharp pebblea
which groove and scratch the rocks bdow. And further, it

BtJDIMBHTAEY GEOLOGY.

169

should be remem be ml tbit when the surface of a rock, laid
bare by the re moral of clay or other matter* is examined, the
results of several successive actions may be manifest, as, for
example, the rocks may liare been polished by the attrition of
sand carried along by ordinary currents, and subsequently
scratched End grooved by the movement of consolidated masses
of day and the sliarp stones imbedded in tltem.

In countries where the tertiary strata are fully developed,
either as deep sea or as great lacustrine de|>osits, they supply
valuable building materials both in limestone and in sandstone.
The fossil bitumen so extensively used in asphalte jmvements,
namely, that of liastenue, s small village of the South of Fiance,
l.i miles north of Orthei, is tertiary. The formation in which
the bitumen is found rests ou a sandy limestone, which lias
been allocated to the cretaceous system, and it consists of
bed* of variously coloured mind* and days, winch are .'ll) or 60
fret deep, and covcrrd by gravrl and sand, which extend many
mile* in r'erv direction. These beds arr usually horicontal,
though sometimes much disturbed by the intrusion of igneous
rocks. I nder almut 4. f » feet of variegated sands and clay*
there is a small quantity of bitumen in a lied of blackish sand
4 feet thnk ; from to IJ* feet of bitumen are then observed,
the upper part of winch is mixed with loose and coarse sand,
the lower being more com|»act t and mixed with finer land. In
some pliers there are 10 to l.j feet of saihI without bitumen,
whilst in of Iters the bituminous sand is thicker, and rests
directly on the secondary sandy limestone. In two locahtiea
manue *helU have been found in the bituminous sand, and
referred by Mr. Pratt to the mtorroe period. The shells are
arranged m Layers, and are quite jwrfrct, the valves not being
separated from each other ; and the bitumen, when in a soft or
liquid stale, was, in Mr. Prmtt‘« opinion, forced into the shells,
after their dr|*>atfion in the sands in which the animals lived,
filling even their smallest cavities. The eruption of the bitumen
is supposed to have been connected with the appearance of
ophite, an igneous ruck which has produced such great clyuiges

170

RUDIMENTARY GEOLOGY.

in the Pyrenees. The bitumen is easily cut when first exposed,
but in a few days it hardens so much as to become incapable
of purification : the purification is effected by boiling the sandy
mixture in a large quantity of water two or three times, when,
by continued and careful stirring, the sand gradually settles to
the bottom, while the pure bitumen rises to the surface and
is taken off. A small portion of bitumen occurs in the ter-
tiary rocks of Anti-Paxo, and again in a larger quantity at
Xante. The existence of gypsum and salt in the tertiary
strata has been already noticed.

Before quitting the remarkable geological epoch embraced
by the tertinrie*, it is desirable again to bring before the mind
the zoological history it has unfolded. Approximated as it is
to the existing world by many still existing species, there arc
sufficient peculiarities to stamp upon it individuality, whether
the lower or the higher portion of the organic creation he made
the basis of comparison. The tertiary world is as distinguished
from tin* existing by its corals as it is by its mammals ; and
whilst it rejects any decided union with either the past or the
present, it manifests numerous affinities to both. In the ttiol-
iusca, the nautdmd tyj>c which flourished in its most extended
development of form in the Silurian ejunh. was still repre-
sented bv two genera. -- at una {clymcne) and nautilus, and
act cu sjM^ies. In the reptdui which swarmed in the oolitic
cfHH'h, ami appeared m> early as the Devonian, the tcrtiaries
were rich, the l#ondou day alone having furnished in the three
families of marine, tluvmttle, and marsh turtles, relics of no leas
than -7 species, and in the marine genus cheloue 1 I species,
whilst in the whole extent of cur present world onlv five
species have ns yet been discovered ; — m the cromdiha, three
crocodiles. one alligator, and one gnvial, some of whu h exhibit
that mixture ot tyjK's which has been noticed in reference to
the combination of the lutard and batraehian types, in the
early reptiles of the old red and carboniferous epochs, in the
Ucertiha, oue true lizard ; and in serj»ents, six species, some
of which were gigantic and probably marine, in

ECDtMXKTAlY CIO LOOT.

171

the more recent deposits, including bone cere*, exhibit tome
specie* which ire yet existing, tuch is the red deer* the mu-
cker, the goat, the wolf, tnd the fox ; others doeely allied to
the existing species of ox, horse, hy*na» rhinoceros, hippopo-
tamus, and elephant, associated with extinct forms ; mini here,
as in preceding rases, particular orders seem to hare attained a
peculiar development, namely, tlie edentata or toothless and
the pachy denuata or thick-skinned animals, including the
gigantic fossil sloth or ntylodon robustum, the mighty d mo-
ther! um equalling the elephant in sue and with tusks turned
downwards as »f to tear up the ground, the hyracothrnum,
anthracothenum, the lophiodon and paheothrnurn, resembling
the American tapir*. the anaplotherium, whieh seems to con*
nect together the genera rhinoceros, horse, hippopotamus,
hog, and camel, “ -and many other extinct genera, liesides the
cetaceous genus mig!t»duii, which may lie considered the
marine representative of tins type. But amidst all the**?
strange forms, including the givptodon or giant armadillo,
there npjnar representatives of that order, the <|iiadruinana t
which at least suggests, even if it caricatures, the form and
art ions of man, in extinct sfwcie* of apes, and rvrn of the
ourang. The hat also had liegun to fht alx»iit m the dim twi-
light of a world which a* yet had not been tenanted by .Man ;
and on every side it appeared that the Creator bad nearly
established that balance in the number*, jwmrr*, and func-
tions of other animals which would render the world lit for
the reception of the greatest work of creative grower - a being
endowed with reason, or with the jaiwrr of investigating and
studvmg his own structure, and comprehending the relations
which connect lmn at oner with tlic great Creator, and with all
the works of creative powrr.

QLATKKHASY, IHiar-TKITI ARY, Oft POST- FLICK: IE I —
fttCKST.

Our inquiry ha* now come to that (aunt where, though we
•till see ui the recent results of geological phenomena tneknea

172

KUDIMKITTAftY GEOLOGY.

of the formative pr o cea a c a of nature, — coral reefs still vising
from the depths of the Pacific, — conglomerates being still
formed in the Mediterranean, — beds of marl being still depo-
sited in lakes, — travertin being deposited from mineral springs,
— and peat being observed to have formed over fresh-water
•hells, the bones of land animals, and even the works of human
art, — we sre still kept at a distance from the recent epoch ;
for although organic relics are all of recent species, they are
generally arranged in positions and associated with detritic
matter of such a description that their appearance indicates
the action of forces prior to the present order of things. These
masacs, the true post -pliocene, though now exposed to view
and frequently found at high elevation* and of great depth, have
evidently been, like the antecedent formation*, under the level
of the water* either of lakes or of seas, whilst true recent strata
are, in most cases, still in the position from which the former
have emerged. To this obscure region must be ascribed raised
beaches or those remarkable accumulations of gravel which
though far above the present level seem to mark the former
posit iou of the sea boundary or short', or which bordering the
aide* of lake* show in like manner a depression of the surface
of their water*. Halted lieaehes, as well a* the pleistocene
deposits, hate been ably examined by Mr. Smith, of Jordan
Hill, who has noticed 130 »}»ecie* of shells in those of Eu-
ropean origin ; but it must be manifest that at this point,
when* the ancient strata are blended with the recent, ancient
beachc* whether marine or lacustrine must be studied in direct
reference to adjacent localities, a* the changes of position or
altitude do not imply an alteration in xoological conditions.

Recent or AlUnul. — The natural phenomena which can be
now studied are valuable guides in estimating those of past
epochs; and by many analogies of alluvial deposit* may be
learnt the mode in which more ancient deposit* have been
formed. The action of rivers may be estimated by the exten-
sion of the deltas at their mouths, and that of the sea observed
in all its phases. The processes of destruction and of formation

KVmXKVtARt OKOtOGT.

173

eonmded with thfw actions extend over the whole earth,
though, being necessarily modified by many local peculiarities
they produce parallel, not identical formations the contempo-
raneity of which it will be difficult at more remote ages to
determine. These formation* mar be divided into mechanical,
chemical, and organic, and alap into land and aea formations
volcanic products being connected with rach.

MerKamtcal Urpoat * — Torrents and rivera, in their ratine
through mountain regions cam- along with thrm a mixture of
large and small fragments torn from the boumUnr it>cks, and
deposit their load in the lower and more tranquil portion of
their course, as gravel, sand, or mud, — the nature of the depo-
sit and the distance to which it is carried being proportioned
to the strength of the currrnt : and this simple and constantly
occurring natural event exemplifies the removal of portions of
rocks from their native lied ami tlirir subsequent de|>o»ition,
and the formation of alternating l>ed« of clay, sand, ami gravel.
When a river passes through nicks rirh in oris or in precious
atones, its waters often separate from their matrix those sub-
stance* wlfirh from their superior weight remain behind, whilst
the finer matter is burned onwards. DrjmsiU of this kind are
valuable from the quantity of ore ami of gem* which they somo*
timet contain, ami which are separated by repeating the natural
process or washing away thr remaining fine matter. Par-
ticks of gold, platinum, indiurn, rhodium, jialbuiium, os-
mium, chrome, and magnetic iron, arr obtained in Wicklow,
in the Crai chain of Russia, in Brazil, in California, Aus-
tralia, and elsewhere ; the trrm stream gold or stream tin,
Ac. being applied to such products. As yet, platinum lias
only been obtained in this secondary manner, and thr greater
proportion of gold is similarly procured, as well as a con-
siderable part of the tin, as also the zircon of Bohemia, the
thrysobenrls and hyacinths of Ceylon, the diamonds of Brazil
and of the East Indies. In Borneo, gold has been found
mixed with alluvial matter in limestone caves. The gravel
•f the Rhine is estimated by M, D’Aubrfc to contain ‘aa

174 ftrDIMENTAKY GEOLOGY.

•mount of gold equivalent in value to 165,828,000 francs, or
j£ 6,564 ,025.

Deltas . — Where riTers discharge their suspended mud into
the aea, and where the coast is shelving, and there is no
powerful marine current, a delta is often formed hr the depo-
sition of mud at the point where the waters have lost their
tranajiorting power. It usually commences at the centre of
the river’s mouth, an island being first formed, which goes on
extending and widening till a triangular space is occupied bv
the deposit, the apex being directed upwards, and the base
faring the sea; and this form having been first noticed in the
mouth of the Nile, the name Delta was applied to it from the
Greek letter of that name. Sometimes, as in the Nile and
the Khine, several islands are simultaneously formed, so that
the delta is finally a rotti|M>und one. and is separated by various
channels. The delta of the Ganges is still more remarkable
than those uf the Nile and Rhine, its perpendicular depth from
the apex to the base being atawt ISO miles, and therefore ex-
hibiting a formation comparable in extent to many of thoac
of past geological ejmehs.

from the act ton of the Sea. — The sea effects a change in the
firm and jxwition of the land with which it is in contact; for
whilst at one |w»iiit its waters encroach upon and carry away
the land, at another they dc|»o*it new matter, and increase it;
and ns they contain from three to four per cent, of various
mineral salts (ns chloride of sodium, chloride of magnesium,
sulphate and carlwmatc of magnesia, sulphate and carbonate of
lime), the formations produced are often more fixed and solid
than those of fresh water. This is socially the case in warm
climates; and as the fragments of shells as well as com-
minuted portions of calcareous rocks are often mixed with the
deposits, sandstones arc sometimes formed, sometimes lime-
atones, sometimes conglomerates. In a formation of this kind
at the Island Grande Terre, near Guadalnupe, human remains
have hern imbedded, and many such are in progress of de-
position below the waters of the sea, and will be brought to

ftCDIMKNTARY OKOLOGY. 1*5

light by such upheavals of the coast and sea bottom as that
which so strikingly affected the coast of Chili.

Chemical Deposits,

Calc T*f and Calc Sinter, or Trarertm . — All spring waters
are charged with mineral matter, which, coming to the surface,
they, in their course, dejKisit by the influence of light, air.
rra(H>ration, loss of temperature, absorption, and escape of
carbonic arid. Cold springs charged with lime yield in this
manner rale tuff, or sinter in tlir form of rale spar, and hot
springs it\ that of arragonitc. ( ale tuff is usually a porous
ma«*. hut sometimes its layers are sufficiently firm to he used
in building, and are then valuable from their lightness. The
most remarkable example of such * travertin* formation* is to
In' found in Italy, and so rapid is tin progress of deposition,
that at the Hath* of San Filippo, a mass, ,'tO feet thick, has
been formed in twenty vear*. These springs are made use of
to procure stone casts, the lime being deposited in a firm and
solid state on models immersed in the water.

SihrufU* Tujf, or Sinter. — Thermal springs deposit much
silex on cooling. The hot springs of Iceland, and especially
the (iexser, are of this description. At intenals of a few
minutes, a lofty column of hot water is thrown up, and then a
dense f«»g overspread* the surrounding ground, and from this
condensed spray the silex i» deposited m the |»orou% form of
tuff, or sinter, whilst, in the interior iff the basin, a *|>ecir* of
opal is formed. In the A tores several springs dej»o*it silex ;
and it is very probable that semi opal and hyalite, which are
frctpientlv found in the crevices of basalt, and, in short, most
of the tiheious rninrraU which are so abundant and so lx anti*
ful in that rock, hare been formed m a similar manner by the
filtration or absorption of the water by which the mineral
matter had been originally dissolved.

Bo$ Iron { Ltmoniic). — Ferruginous springs or water* de-
posit a brownish red scum of peroxide of iron on their banks,
or at the bottom of bogi and marshes masses of iron ore,

176

RCDIMCKTAKY GEOLOGY.

which ha« been called from such localities bog or marsh iron ;
and ai sand or gravel mar be mixed up with and consolidated
by the mineral matter, a variety of iroastone is formed, whkh
has been called sand ore. In Sweden, bog ironstone has been
ftfthed tip from under the sea, where, according to Uaustnann,
it is still produced, and it would be interesting to compare the
microscopic structure of tin# ore with that of fresh water.
The presence of phosphoric acid in bog iron ore, so unfavour-
able for smelting, is probably due to the decay of organic
bodies in the water duriug its formation.

Deposition of Saline fkxhea . — The saline deposits thrown
down by springs, streams, and lakes are not extrusive. From
the mineral springs of the Baths st Vienna is precipitated a
fine powder, consisting of gypsum and muriate of lirne. Ill
the South of Husain, several lakes annually overflow their
banka and dr|*»#it a saline cruwt , a phenomenon which is much
more common in the lakes nud in the very low grounds of the
wanner roues. In Kgypt, soda has in this manner Urn de-
posited in Urge quantity. The extensive turf moors at Fran-
arnshad, near Kger, are partly eontrd with a white saline crust
of sulphate of soda (Glauber salt) and sulphate of iron. Some
salts exude out of rinks, as salt | N't re (nitrate of |H>tash or
nitre), in the limestone caverns of Braid and of Ceylon.

Mineral (hi, or Fitch — In several parts of the earth there
are spring# of a mineral oil which on drying becomes either
asphalt? or a species of roalv mass. The Carpathian* and the
vicinity of tlie Dead Sea are rich in these springs, and iu the
bland of Trinidad they almost form a sea of asphalt? .

Organ ir Formations.

Turf. — This vegetable formation is sometimes covered by
more modern mineral deposit* of little extent, and sometimes
exhibit* a passage into brown coal. Turf cotiibts principally
of an accumulation of marsh and water plants, especially of
various species of moss, the lower layers of which have in suc-
cession died, and through the action of humic acid been

RCDIMEKTARY GEOLOGY.

177

changed into * peculiar brown, felted, slimy, ami combustible
man In some livers of tnrf. the remains of plant* are so
decaved and changed tint their oritcinni condition can only lie
iiifmed, but in others the actual jqwcies of the moss can yet
be determined. In some bogs, the growth spj>ear» to have
ceased, whilst in others vegetation is still vigorous on the
upjK-r surface. In Alt -M’arinbrucher moor, near Hanover,
cutting for the second tune, the turf has Iveen re-formed,
according to Lcouliard, in fifty years, a layer from I feet to (»
feet thick having been in course of fonnatiou during the last
tlnrtv years. At Fraturnsbad, near Kgrr, a similar fact has
been observed, the exhausted turf hollows having hern again
filled with new turf plants in from ten to twenty years, which
art formed into useful turf tn from fifty to one hundred years.
The treat of Ireland are amongst the finest examples of
tins kind of formation, lw»lh as regards their extent and depth ;
and although no very detailed or satisfactory obsen at ions hair
been made on the new growth of hog in old exhausted hollows,
where drainage and cultivation have not so modified the con-
ditions as to stop it, a very slight observation is sufficient
to show that the first step of the accumulation of moss
plants can vet In* traced. Keferstein has remarked that turf
formations are rare on calcareous and frequent on adiriotis
bottoms, hut Ireland is at least an exception to this rule, as
turf is abundant in some of the limestone districts, and hat in
several cases grown over lacustrine dcjxMufs of shell-marl.
Thick beds of turf occur on the summits of some high bills tn
Irrland and other countries, where a clay bottom retains tins
moisture. On the banks of the North Be*, a species of turf
is formed from accumulations of sea weed. Large masaes
of bog have sometimes been detached, and become floating
islands, one of which, on the Gtaiaurr lake, in Prussia, was so
large as to support a hundred bead of cattle, until, in 1707 , it
was broken into three parts by a severe storm. Sometimes
turf is (bund below the high-water leva! of the sea, as at
Grafswald* and Geagrland, on the East Sea, and on the north
■ 6

178

RUDIMENTARY GEOLOGY.

coast of Ireland, near Portrush, where the elytra of beetles
(still fresh ami bright) occur between layers of turf. Turf i*
also formed in the warm zones, as at San Paulo in the Brazils.
In the Irish bogs, the roots, trunks, and fragments of the
branches of large trees, both oak and fir, are abundant, and,
in sewral instances, two or three successive sets of the roots
stand upright one above the other. Turf affbrds a connecting
link between the existing rjiorh and the next preceding it. It is
sometimes very compact and full of iron pyrites which fre-
quently induces sjiontancou* combustion and the formation of
sulphates, often contains fresh-water shells and is covered by
layers of sand ami clay, and as it passes into brown coal is
more nearly connected with the diluvial than the alluvial
section of the post-tertiaries. A bed of turf with stems of
trees has U*cn found under a covering of lU feet of sand,
and 7 feet of earth ; and at Wittgemlorf also, near Sprot-
tau. in Silesia, turf rests cm fresh-water marl, and is
covered with sand and gravel. A wooden bridge, made bv
Germanirus in his German war, was found under a Img ;
and in Galway, a hut and paved passage was found under
30 feet of hog by the late Capt. Win. Mudge, It. N., both
Wing interesting examples of the manner in which such
formations, when unrestrained by cultivation, spread over and
deform the surface of the earth. 'Die growth of sphagnum or
ln>g moss being most rapid in the centre of a hollow, where
the moisture is greatest, bogs are generally much swollen in
the middle, and go on increasing in height and thickness until
the slope ia sufficient to discharge the waters and limit the
growth. Examples are cited where towns once visible front
each other, are now shut out from view by the elevation of a
turf mots between them.

Smlmmrimt fores/s. — On various parts of the coast of Great
Britain and of the North of France the remains of ancient
growths of trees and plants are found in positions below the
level of the sea, though bel o ng in g to species still firing. They
art sometimes exposed by the encroachment of the sea ou the

RUDIMENTARY GEOLOGY.

1/9

coast, and at other tiroes simply by the ebb of the tide, and
probable owe their present position to a partial depression
of the land : General Lewis has noted a fine example of such
forests on the western coasts of Jersey.

Coral Her/s ami Islands . — They prevail in the Pacific and
Indian Oceans and in the Red and Mediterranean Sens, Re*
cent researches, especially those of Quoy, Gainmrd, and Lhrcn-
Ix-rjcr. have shown that the growth of coral docs not continue
in great depths, and that coral reefs or islands arc generally not
more than JO feet or dO feet thick, and are onh incrustations
on the inequalities of the sea bottom, whether formed on
mountain masses not yet elevated to view, nr on banks of
detritie matter. Whilst, then, such formations explain the
nature of the true coral reefs of ancient epochs, and account
for the deposits of shale with calcareous lasers of corals so
common in the carboniferous system, the formation of the
greater masses of limestone cannot he ascribed to the acliou of
coral -poly pc* alone.

Infumna.— Some masses of rock consist of little else than
infusorial remains, as tripoh, jxdishmg slate, »Vc. Sometimes
the infusoria which have formed these strat/i belong to extinct
ami sometimes to still living species, so that the microscope,
guided by Khrenberg, confirms the reasoning on successive
creations which had been founded on the contemplation of
higher organisms. The silieious skeletons of these minute
beings are accumulated at the Ixittoms of marshes and stag-
nant waters, as in the turf moor near Eger, and thick !>eds of
a white silieious powder are thus formed, consisting of the
unnuird silieious portions of still existing infusoria. Some of
these infusorial substances, such as tnjxdi, polishing slate, 4c.,
haxc been classed with mrtjds. from their gtmrral appearance,
hut their true character has now been revealed by the micro*
scope. Moat infusorial drfxjsiu probably belong to antecedent
epochs, hut that of Egrr is evidently recent, and iu all coun-
tries where waters flow over much decomposing silieious rock
infusorial formations may be expected.

180

RUDIM K5TARY GEOLOGY.

Landslips arc also phenomena of the recent, although with-
out doubt they hare occurred also at ancient epochs. Where-
crer a soft stratum is liable to be removed by the action of
percolating water, slips in the harder superjacent rock are
common, as in the Isle of Wight, &c. They are finely ex-
hibited in Ireland, where the soft basic and oolitic beds being
removed or squeezed out from below the basaltic cap which
coders the cretaceous and subjacent strata, the top cracks
and slides down, as in fig. 18, which is a portion of the basaltic
escarpment of the North of Ireland.

fig. 18 .

RUDIMENTARY GEOLOGY.

181

CHAPTER VII.

Thro 17 of Spring*.

An water is the most important substance in nature, being
the solvent by which nutrition is conveyed both to the plant
and to the animal, as well as the chief agent by which the
mineral kingdom has been again and again both abraded and
restored, it is desirable to consider that constant change and
movement bv which its purity and fitness for performing its
several functions are insured. The ocean is the great recipient
of the larger portion of rivers and streams which flow over the
earth’s surface, and its waters arr in constant motion, the
warm currents proceeding from the Equator to the Pole, and
the cold from the Pole to the Equator ; whilst evajioration
cause** a pcrj>etua! movement of vapour upwards, which, being
condensed, falls in rain upon the earth, ami again returns to
the sea. These simple processes bring within the reach of
organic action a constant supply of this vital fluid in a pure
and efficient condition, as springs, rivers, or lakes. The useful
distribution of water is promoted by the physical inequalities
of the earth; for had its surface been uniformly level, the
filling rain would have soaked and saturated the upper strata
to as to produce a swampy condition, not probably very dis-
similar to that it actually possessed, over large tracts, in the
earlier geological epochs. The conjoint actions of elevating
and denoting forces have, on the contrary, produced chains
of mountains, valleys, basins, and all the minor modifications
of these three great forms. In the vicinity of mountains, the
effect of this arrangement is readily observed in the river
which one day straggles with its riband-like stream through

182

RUDIMENTARY GEOLOGY.

a wide bed of stones ami gravel, and the next rushes forward
an overflowing and turbulent stream, having been swollen by
sudden rains which, falling within the area of its connected
vallevs, had l»een collected into one great liquid mass within
its bed. The more numerous the feeders and the more closely
connected with mountain masses, on the summits of which a
very large portion of moisture is always deposited over a com-
paratively small spare, the more sudden will l>e the rise of the
discharging or recipient river. A large portion of water is
thus carried off directly by running over the surface, but
another large portion percolates through the surface to a
greater or lea* depth, in projHirtion to its porosity. In clayey
soils, this passage of the water is very slow', the surface in wet
weather Incoming moist ami clammy, whilst in dry, it forms a
crust fissured by cracks. In sandy or gravelly soils, the pas-
sage is very' quick, and the surface remains comparatively dry ;
but where the soil is not very deep, and part of the water is
retained by a more retentive substratum, the moisture is
readily restored by a continued cvaj>oration and an injurious
aridity is prevented, this condition of the surface being more
generally favourable for vegetation than an impervious soil.
Where, on the contrary, the sand or gravel is very deep, and
rests on an inclined surface, it ads as a filter, and a general
aridity of surface is produced by the rapid removal of the
water. These consideration* naturally lead to the following
theory of Springs.

1 . Whilst part of the rain which falls on the surface runs
off as on an inclined plane, another part filters through it, and
when collected together in any cavity of a less pervious sub-
stratum, forms a reservoir of water. Even on the aides of
mountains, especially in damp climates, this process may be
observed, for, whilst the general surface becotn^g wet and
boggy, wherever an inequality has led to an accumulation
of water, numerous springs are seen issuing as scarcely per-
ceptible rills, which gradually increase as they join with
others, and finally emerge in the greater valley as con-

rudimentary geology.

183

siderable streams. Such is the most simple ami ordinary form
of springs, from which may be derived every other, by taking
into consideration the peculiar modification in each case
of the earth’s surface; and springs arc therefore superficial,
small, numerous, ami very temporary, where the previous
stratum is very shallow, ami the inctjiiahties of the sub-
stratum slight.

‘J. In addition to t lie water which forms the superficial
springs on the mountain side, a portion may pass between the
underlying rock and the superficial matter almve it, whether
the latter lie a stratified deposit or ordinary detritus resulting
from the simple decomposition of tin* rock itself; or should
the overlying dejwisit Ik* moderately porous, some of the water
may pass directly through it to the underlung rock, where
resen oirs of water will he formed in its hollow* or depression*.
This i* n case which occurs eten m granitic and highly rncta-
morphic rocks ; and ns open fissure* are rare in grnintr, whilst
su|M*rficiftl disintegration, especially in hot countries, has pro-
ceeded to a great extent, it afford* almost the only chance of
meeting with deep-seated springs. Colonel lladdrly, It. 1'.,,
has shown its application and explained the principles which
regulate the appearance of springs in Ceylon. The under-
lying rock is a highly metamorphic homhlendic or sveniti/
gneiss, the outcropping edges of which having undergone much
original modification, arc supposed to form an undulated sur-
face — thus, in fig. 19,

Pi*. 19.

184

RUDIMKKTAftY GEOLOGY.

the hollows being filled up by a detritus, proceeding, according
to Colonel Baddely, from the simple disintegration in situ of
the more fdspathic surface. From the mere inspection of the
figure, it is evident that whatever may be the origin of the
matter filling up the inequalities of the underlying rock, the
water, either in part percolating through it, or passing between
it and the surface of the sound rock, must accumulate in the
hollows, and that in consequence it would be necessary to sink
at b to HO feet for water, although at a it had been found at
40; and further, that should the rock under b slope gradually
off, and become exposed in a valley, or on the side of a hill,
the water may all he carried off as quickly as supplied, and
produce therefore no jiennancnt spring, — circumstances which
render the search for water very precarious. It may be
further added in resj>ert to this example, that a rising or
projecting spring can only be expected where the water pass-
ing between the detritus and the rock is |>eiit up by them,
and thus affords a head of water ; as if it merely filters through,
the pressure can only raW the spring to the height at which
the water stands at the time in the resenoir or hollow. The
other form of this rase is, where the hollows of the crystalline
rock are filled by stratified deposits (No. 20) of shale and

•and. Here, as the shale has been worn away, and the rock
denuded at the summit, the water may gain access to the
layer of sand (#*), and produce therefore a spring under the
bore-hole («), the water being held back by the projection of

RUDIMENTARY GEOLOGY,

m

the rock to the left of it. When the water has saturated the

whole of this stratum, it will
hut as the stratum is open
to the ralley below, it will
be rapidly discharged, and
produce uo permanent spring
under the bore- hole (6).
Again, under both a and
b, there will be a second
supply of water due to the
sand stratum (r ) ; but as
these lower reservoirs from
their imperfect connection
with the surface must require
a considerable time to till,
their practical value will l>e
in proportion to their mag-
nitude, or to the quantity of
water stored in them. ^

3. In the preceding in- £
stance*, the accumulation of
water has been considered
to arise principally from that
which flows over the under-
lying solid rock, hut it may
Ik* entirely due to that which
enters directly from the stra-
tified deposits, and in merrly
held hark or dammed up by
time rock, as in No 21.

Here it is evident that the
supply of water will Ik in
proportion to the extent of
surface on winch tin* rain
fails, and from which it ls
directed to the layers of sand

rise over the projecting rock;

186

RUDIMENTARY GEOLOGY.

(a 1 and a 2 ), the remaining maw being either clay or some other
impervious stratum. If the supply be abundant, the stratum
will be kept saturated up to the line of the bore-hole (a), and
a constant spring be obtained ; but if it be only small and

casual, there may be a spring during
the rainy season, or whilst the water
is making its way through the stra-
tum, but none at a later period, and the
chance of permanency will lie increased
as the bore-hole is carried nearer to
the rocky dam at and the wune
reasoning will apply to the upjier
stratum of sand (#■), and its bore-hole
(4): and it may lie ohaenrd also, that
a bore-hole (« ) by which a tenijw>-
rary spring only had been (bund in
r\ by being carried through the in-
tervening clays, would obtain a per-
manent one in

This case lead* to those where the
water i* receded and thrown up en-
tirely by stratified deposits arranged
in the form of basins or troughs,
which may happen either where the
basin is produced by an undulation
or depression of the uiiderh ing strata,
or where it occupies the t alley pro-
duci’il by the disruption of these strata
on elevation ; ami as some precaution
is necessary in reference to this dis-
tinction, each case will be considered
separately.

No. 22 is the first rale where the

strata of sand and clay liave been

deposited in a basin of undulation, and the water entering the

aand stratum (a) is presented from descending by the imper*

RtT D1MKNTAKY OKOLOQY.

187

rious strata below, and from
amending by the clay above ;
so that it is pent up in the sand
stratum itself. An insj>ectiou
of the figure is sufficient to
show that the nearer the bore-
hole is made to tin* lower point
of the valley, the more abun-
dant and secure will l>e the
supply, and the higher the jet
from the aperture. If. instead
of one layer of sand or gravel,
there had Wen several, the
reasoning would he the same,
only it might happen that the
upper layers, closed up by the
clay passing over them, as in
the figure, would be found un-
productive of water, or that
two lasers of clay might romr
into contact u.th each other,
and shut out the sand, rases
which have Wen illustrated by
recent borings at Portsmouth.

No. 2d is a basin formed
within a vailev of disruption or
even of denudation, nr winch
differs from the preceding only
in this circumstance, that the
boundary walls, as it were, of
the valley may in themselves
he f*artly pervious, and there-
fore allow the water to r*caj>c.

If such occur, the water cannot
rise above the level of these
discharging strata, represented in

186

KVOmilfTlKT GEOLOOT.

secondary denudation may modify the basin deposit, and affect
its supply of water, as in No. 24, where it is evident that any

fif. 24.

layers of sand rut through bv denudation in the centre of the
basin must discharge the water they receive at once into the
inner valley of denudation, and that no water can be exjieetcd
until the lower layer, or at least the first layer not affected by
the denudation, has l>ecn tombed by the borer. Faults may
also materially affect the arrangement of springs, as in some
eases when tilled by impervious matter they act as dams, and
in others discharge the water, — so that in lKiring in the
vicinity of a fault, care must he taken to ascertain its condition,
and if it l>c *tip)»oscd open, to place the bore-hole in the strata
dipping frum \t .

It is conceived that these examples are sufficient to explain
the application of principles to practice in c*\cry case, and to
show the great necessity of studying the geological as well as
the physical ebarartrr of a country in which water is sought
for. In granite, and in most cry stalline rocks, a search for
water must l>e very precarious, as it can only occur in or
connected with fissures. In stratified deposits, not meta-
morphosed, the occurrence of alternating porous and iuij»er-
vious beds brings the principle into operation ; and in pro-
portion as the }K>rous beds arr looser in texture, as in tertiary
and post -tertiary sands ami gravel, and the arrangement
assumes a baain-like form, will the chance of success increase,
and a correct knowledge of the stratification at the out-
cropping of the strata must therefore be the surest guide.
In boring, the strata passed through should be compared with

MUDIMKNTAEY GKOLOGY. 189

those visible on the surface, in order to judge what specific
stratum has been arrived at or passed through. Should there
be no basin-like deposits of looser materials, the pursuit of
water in more solid strata must be equally guided by a know-
ledge of their geological and physical peculiarities ; as, for
example, in the chalk and even in the oolitic districts, where
numerous futures allow the water to descend, until it is stopj>ed
by either a less fractured bed or by some of the divisional
clayey beds of such formation* ; and when once such ImhI or
stratum has been discovered in any district, it becomes an
index for the operations of the borer.

Although the several methods of boring cannot be here
described in detail, it may be well briefly to notice the most
remarkable. — 1. The common one, in which an auger is used
for soft noils, ami chisels or junipers for rock*. In this iiukIc
the boring tool is connected with the surface In jointed rods,
fastened firmly together, am) which must be frequently raised
to clear the hole of the debris ; so that in gn at depths the
weight to he raised and the time lost in separating ami re-
filing the joints become sources of great expense. — 2. The
C hinese mode, by perm* Mon alone , the borer itself weighing
al>out ISO Jh»., and being suspended by a coni, is alternately
raised and allowed to fall, the debris either passing up through
grooves in the sides of the tool and being thru drawn up when
accumulated on the bend, or received into a separate cylinder
with a salve oj>ei»ing from 1k*1ow upwards. This method is
much more economical than the common, and has lweti used
verv extensively in (iermany, though it is subject hi two
accidents requiring great precaution, sir. the great difficulty
of drawing up a broken borer, and the danger, from the
flexibility of the cord, of the borc-holr taking an oblique
direction, ami therefore requiring to l>e abandoned l\. The
system of Fauwdlc, in which a hollow borer, either an auger
or a jumjier, is used, the cutting tool bring of Larger diameter
than the hollow stem, so tiiat an annular spare is formed
around the borer , and water being forced down thin space by

190

EGD1MEKTAEY GEOLOGY.

a force- pump, ascends by the tube, bringing with it all the
ddbris, or if forced down the tube, ascend# in a similar manner
by the annulus. As this arrangement renders it unnecessary
to bring the boring tools which are constantly kept clear up
to the surface, a vast saving of time and expense is effected.
The cities of !«ondon, Paris, Vienna, aud Mentx are on tertiary
basins, and the first two are now supplied with the moat
wholesome jmrtion of their water by Artesian wells; the
borings in the Ixmdon basin passing through the l^oudon
clay, which only yields impure mineral springs, and finding
water either in the sands of the plastic clay, or in the fissures
of the upper surface of the chalk.

In tracing out the sequence of strata which have now been
passed under review, it is scarcely necessary to say that the
Geologist should base his hammer almost constantly in hand,
and will find it often desirable to use some description of
clinometer in unravelling the intricacies of stratification. It
is unnecessary to descriltr the hammer, as geological hammers
can now l>c readily procured, and the form itself should he
varied to suit the nature of the rock ; or to figure anv complex
clinometer, as the observer may attain his object by scry
simple contrivances, such as a small wooden quadrant with a
pliunb-t>oh and a common junket compass, — minute preciaiuu
being unnecessary.

imiKTAIY GKOUW1.

191

CHAPTER VIII.

t uociiMlift* Remark*.

Tliotnil it i% hoped that thr ftkrtrh gnrn in thr preceding
jiagr* of tiiii n»*»*t mtrrrMun: Science will hair matt*’ it*
leading principle* familiar to tin- reader’* itimd, it mat not lie
U*rlr*% to rrcnpitulatr some of them, nod to *Ugge*l that
caution which i* ncer**ar\ l*»th 1 >r thrir right perception mul
their correct application

Scdimrntan drjuwut* mn*t l*r *t tidied in their mineral con*
(litHm, m th<ir orgntnr !o**d*, and m tin* order of thrir *tr«th
taatioii. The tmnrral condition t% an mdimtion of the ph\%icul
nrcum%tancr* whuli regulated thr dr (Hunt and *o nfhrfrd
irgctahlr and animal lito a* to pralin e a jerutmr local flora
ami tauna . hut thr phi m at condition of thr earth * *urfarc
anil thr n rrn in *t alter* rotmrrtrd with it hating frequently
*anr*i m time and place, thr mere mtnrrai condition of a
at rat mu i» imuflirirut to determine thr cjkm h of it* dr}*>iti>
t«m.

Thr organic fr«**tU represent thr flora And fauna of the
rpovh of dr|wi*{Uon, hut thr law* of or game drrrlopmrnt arc
m>t tufluir nth known to enable thr Naturalist to tuitiinr from
jmrr/y oryaair rr moderation* that any one generic or *}Krific
form must ha*e prccrtlrd cirrry other, and hence thr foaaiW
alone are not auflicu'iit to detrrmmr a geological rj»otdi-

Order of ttratiflcmuon, a* it embrace* tlie examination both
of the mineral and organic eendmou* of a drpotit at iu aue>

192 ftVDlMEICTAftY GEOLOGY.

ctssive stages, or, in other words, of the physics] and organic
relations of the successive periods of deposition, is the only
sure guide to the first determination of geological epochs. In
applying it to this purpose, however, care must be taken to
avoid those sources of error which have been pointed out ; or
to study stratification in districts which have not been thrown
into confusion by disturbing Torres, as the contortions they
produce often place, to all appearance, the newer strata Mow
the older, and sometime* invert a whole series of drj>osits.
The relative ages of geological epoch* being once established by
the study of undisturlied districts, a clue is obtained by which
the confusion of contorted strata may be reduced to order.

The natural progression of organic beings in sjiace and
time as represented by their lateral and vertical extension
in geological strata has been sometimes violently interrupted
by an elevation or depression of the strata by which the physi-
cal conditions required by such organism* were suddenly
changed ; a fart well exemplified at t he junction of warow/urwt-
alle formations : but llu* i* not always the case, and in districts
therefore which hair not been disturbed at t ha in terv nllietween
two successive formations, audin which the suf>erior formation
is com/ormubJr to the inferior, the interruption of organic
progression is due either to a gradual alteration of physical
condition as to depth, or to a rliangr of climate, or to both
continued. In the case of violently interrupted progression
there will lie an abrupt and marked change of xnologiritl cha-
racters ; in that of a gradual change of physical condition, an
equally gradual change of mologieal character ; in the one a
sudden alteration of formation, in the other's transition. In
the present state of natural operations, a gradual alteration
appears to be the ordinary rule, and abrupt alteration, the
local exception , and the labours of some modem Geologists
have tended to establKb the tame deduction for the former
epochs of the Earth's History.

The conditions of the earth which favour the continued ex-
istence of any speeshe organic form art now different in various

BV DIM ENTARY GIOMHiV l!)3

parts of it* surface ; nor nn it be sup)M*cd, d pru>n, that at
a«j epoch these conditions were perfectly uniform ovrr the
whole surface. And further, in the gradual progress of the
earth to a state fitted for the reception of orgainr beings. it is
reasonable to hcheve that some portions must hare become
habitable before others, the progression taking place from
tlie Poles to the Equator, which is rrndeml more probable by
the greater development of the earlier fowsdifmm* formations
in both high northern and southern latitudes. Where dis-
turbances by elevation had lwgun to alter the pin steal con-
ditions of the surface, and to modify the distnhution of sra
and land, the natural organic progression must hare heen
interrupted ; hut wherever such violent actions had not co-
operated with the gradual change of tetri |>crat tire, it is reason-
able to infer that the lateral and vertical extension of many
organic bodies may have brought them into new jw notion* on
the earth's surface long alter the conditions ticrcMary for their
continued existence had ceased at the original centre of their
creation, and thus the characteristic organisms of one formation
may appe ar at the epoch of anotlter : hut a mixture of charac-
teristic forms of the new with those of the old formation will
he usually found to explain the true state of this case. It is
not therefore surprising that a carboniferous Dora should
appear in the Silurian, the Devonian, the carboniferous, and
even more recent formations, although there rau be little
doubt that in each case careful observation will discover the
nrw organic types winch eharartenxc the etiange of epoch.

This difficulty of always determining the actual simultaneity
of apparently similar formation* in no respect affects the
practical application of Geology. In limited countries, such aa
Great Britain a ml Ireland, the physical conditions cannot hare
varied so unequally as materially to protract the existence o t
organisms in one place more than another ; ami hence the order
of geological formation being once well established in one dis-
trict, it becomes a certain guide to the examination of any
other. in more enlarged spaces, though synchronism of

I

194

RUDIMENTARY GEOLOGY.

formation may not be established, the organic group which in
one country co-exists with some definite product being dis-
covered in another, it may be assumed as at least probable
that the associated product will also be discovered.

Vast masses of strata which were once apparently stratified
deposits hare been so metamorphosed or changed that their
original structure can no longer be recognized. Experiments
in the laboratory hare proved that similar changes can be
effected on the small scale ; and it is reasonable to conclude
that the long-continued ami intense heat of the earth acting
under pressure upon stratified deposits was sufficient to reduce
them to the condition of the crystalline schists.

Hocks which had been in a state of igneous fusion can be
traced from the earliest epochs, and they are found to graduate
into the true volcanic rocks of the present time. The effects
they have produced on some of the strata frequently determine
the epoch of their appearance, but there is often much diffi-
culty in determining the relative ages id* such rocks, and still
more the depths from which they have proceeded. It haa
been here suggested that specific gravity may possibly afford
the safest method of solving such questions, and m conformity
with such rule, that granite has probably proceeded from a
leas depth than moat of the |K>rphyries and basalt*.

The penetration of strata, in the form of dykes, by igneous
rocks, the contortion* of the strata, ami the elevation of
mountain chains, arc so many proofs of the operation at
various epochs of disturbing forces, llie results of which arc
still observed in volcanoes and earthquakes. If the primary
cause of such disturbances be the pressure of the solidifying
and contracting crust upon the still liquid nucleus of the earth,
it is reasonable to bebeve that the intensity of the elevating
force should increase with the augmenting thickness and pres-
sure of the contracting crust, though the quantity of matter
erupted may decrease ; nor is this inconsistent with facts, as
some of the greatest mountain chains hare been derated at
comparatively recent epochs, whilst the ancient basaltic Hows

KUDIMIVTAKY GEOLOGY.

195

appear to have Wti* as a whole, more extensive tluui those of
recent volcanoes. In resj>ert to contortions, they may be either
explained a* the result of pressure on the solidifying strata hr
the wa* e-like movement ol* the disturbed fluid mutter, or he
considered, according to the theory of IVibwor lingers, to
represent the wase itself continued mto the crust. To Pro-
fessor linger* is due the most bdmrtuus and accurate ex-
amination of the fact* ot contortions, and a most |>crqneuous
enunciation of his thron founded iqxm them, hut it is very*
doubtful whether Any simple oa\c of translation of n dense
liquid mass ran be made to nuilorm to the tnrtrd form* of
contortion. Whilst, then, such swells of the comparatively
level •urfarr, ns base been demonstrated bv the |>cmhi!um
dcdm'Jeu* of M. Uoirt may be reasonably considered smr»
conbrrmmg to those «»t the inpod mu lt us, contortion* an'
fiujre probably the effect of j»rcs«mre on strata, ahu ll not
being suflinnitly dash* cither t<> follow t lie movement of the
liquid *«»(’, or to transmit the vibration or quake o( a solid
medium, arc folded together.

Iu studs mg many natural phruomcmi, such for rxnmple as
denudation, the apparent magnitude of a result should not be
allowed to oppress or perpb \ the intml, a* it must l»c remnn-
berrd, that though almost immeasurably sast in the limited
perceptions of man, tin s are atomic whrn compared to the
magnitude of the earth it ss if . but this l* Hot the cgse as
rrgmr«U the estimation of forces in the explanation either of
wrar or of contortions, as the law* of matter are uniform and
general, and the force of gravity may lie studied as well in the
fail of a pebble as in that of a mountain, or the magnetic force
of the earth estimated by the vibrations of a needle. The phe-
nomena stand forth as facta to be observed and studied ; but in
seeking to explain tliern, no supposition of unknown forces,
immense m projiortion to tlie forces we tee art mg on l lie earth
as the earth itself is to the mountain which studs or the valley
which dimples its »u riser, ran be admitted. The density of
the earth, and the laws which regulate iu motion, are known,

196

EtOlMEXTAKT GEOLOGY.

End the general properties of matter, whether at rest or in
motion, are also known ; and it cannot therefore be said that
the elements are wanting for the full elucidation of all physical
phenomena, or that any theory is fully established which
cannot be shown to conform to known physical laws.

THE END.

f.C

WImOAmOm*.